Sql-server – Behavior of case sensitivity of RAISERROR when run remotely

I can reproduce this but I think you have a few options:

• not worry too much about full-text index bloat. Not many people are going to be searching for 'rtf1', 'pard' or 'wmetafile0' and I don't think it will affect your performance that much. You might get the odd clash if someone is searching for 'red' or 'blue' but I'd say this is fairly low risk.
• Clean the string up eg with RegEx I copied from here. Seemed to make a good go of it. Store it in a separate table with the stream_id ( which is the unique id for the document ) and full-text index that table instead:

-- Convert rtf to plain text
SELECT 
    CAST( file_stream AS VARCHAR(MAX) ) original
    , MDS.mdq.RegExReplace( 
        CAST( file_stream AS VARCHAR(MAX) ), 
        '\{\*?\\[^{}]+}|[{}]|\\\n?[A-Za-z]+\n?(?:-?\d+)?[ ]?', '', 1 )
FROM dbo.Documents

• Similar approach with a CLR function I adapted from here:

using System;
using System.Data;
using System.Data.SqlClient;
using System.Data.SqlTypes;
using Microsoft.SqlServer.Server;
using System.Text;
using System.Linq;  // for TakeWhile

public partial class UserDefinedFunctions
{
    [Microsoft.SqlServer.Server.SqlFunction]
    public static SqlChars rtfToText( SqlChars inputRtf )
    {
        // RTF function lifted from here and adapted for SQL CLR:
        // https://stackoverflow.com/questions/23277178/richtextbox-throws-outofmemory-on-azure

        bool slash = false; //indicates if backslash followed by the space
        bool figure_opened = false; //indicates if opening figure brace followed by the space
        bool figure_closed = false; //indicates if closing brace followed by the space
        bool first_space = false; //the else spaces are in plain text and must be included to the result

        if (inputRtf.Length < 4) return new SqlChars ( string.Empty );

        int i = 0;
        i = inputRtf.ToString().IndexOf("\\pard");
        if (i < 1) return new SqlChars(string.Empty);

        var builder = new StringBuilder();
        for (int j = i; j < inputRtf.Length - 1; j++)
        {
            char ch = inputRtf[j];
            char nextCh = inputRtf[j + 1];

            if (ch == '\\' && nextCh == 'p') // appends \n if \pard, except for first
            {
                if (j > i && j < inputRtf.Length - 4)
                {
                    string fiveChars = inputRtf.ToString().Substring(j, 5);
                    if (fiveChars.Equals("\\pard"))
                    {
                        builder.Append("\n");
                    }
                }
            }

            if (ch == '\\' && nextCh == 'u') // to deal correctly with special characters
            {
                string fourChars = inputRtf.ToString().Substring(j + 2, 4);
                string digits = new string(fourChars.TakeWhile(char.IsDigit).ToArray());
                char specialChar = (char)int.Parse(digits);
                builder.Append(specialChar);
                j += digits.Length + 5;
                continue;
            }

            if (ch == '\\' && nextCh == '{') // if the text contains symbol '{'
            {
                slash = false;
                figure_opened = false;
                figure_closed = false;
                first_space = false;
                builder.Append('{');
                j++;
                continue;
            }
            else if (ch == '\\' && nextCh == '}') // if the text contains symbol '}'
            {
                slash = false;
                figure_opened = false;
                figure_closed = false;
                first_space = false;
                builder.Append('}');
                j++;
                continue;
            }
            else if (ch == '\\' && nextCh == '\\') // if the text contains symbol '\'
            {
                slash = false;
                figure_opened = false;
                figure_closed = false;
                first_space = false;
                builder.Append('\\');
                j++;
                continue;
            }
            else if (ch == '\\') // we are looking at the backslash
            {
                first_space = true;
                slash = true;
            }
            else if (ch == '{')
            {
                first_space = true;
                figure_opened = true;
            }
            else if (ch == '}')
            {
                first_space = true;
                figure_closed = true;
            }
            else if (ch == ' ')
            {
                slash = false;
                figure_opened = false;
                figure_closed = false;
            }

            if (!slash && !figure_opened && !figure_closed)
            {
                if (!first_space)
                {
                    builder.Append(ch);
                }
                else
                {
                    first_space = false;
                }
            }
        }

        // Return
        return new SqlChars(builder.ToString());
    }
};

I'm sure this isn't the world's most efficient CLR function but it did an ok job on some 100 documents I tested, with a few fails.

Let us know if you hear anything back on the connect item.

There is a connect item discussing (well discussing...) exactly this issue, so it appears to be a bug.

Text 'xp_cmdshell' causes transport-level error: semaphore timeout period has expired from remote system

It appears that the string causes problems, not only in comments but also anywhere it's used as an exact string so even

SELECT 'xp_cmdshell'

results in the same error according to the bug report.

So it appears that the exact string xp_cmdshell is indeed the problem, unfortunately the connect item is closed as "not reproducible".
That being said, I can't reproduce it (on a local connection) on my SQL 2014 (12.0.2000.8, Windows NT 6.3 (Build 9600: )) test system either, so the operating system is probably relevant. Executing the query from a local management studio vs over the network might also be relevant as noted in the connect item.

So you could either work around it by changing the exact text (as you did) or try to reopen the connect item or file a bug report through Microsoft Support.