In the past 7 days I have updated to Xcode 5.1 seven times!
Yesterday I dragged Xcode to the trash and emptied the trash in an attempt to make it stick, this morning I got a popup saying that Xcode had been auto updated (should it even do that?) EDIT it is a preference setting!) but there is still an update showing Xcode 5.1 as being available.
I have now dragged Xcode to the trash, emptied the trash, rebooted and fixed permissions. Noting the previous thread about repeated updates I have enabled the App store debug menu and cleared cookies and reset the application. In desperation I even shutdown my NAS which has the old version of Xcode on it (I invoke Time Machine manually)
I am trying to resolve an issue with my ISP and this is not helping. Before I install Xcode for the 8th time, is there anything else I can do to convince the App store that it has indeed updated Xcode?
EDIT: Despite the above preparations, I updated Xcode just now and another update is already showing as being available!
EDIT: I may have solved the problem. Another application needed updating and then also exhibited the repeated download issue. Reading around I discovered comments about Spotlight and App Store issues. The Spotlight fixes didn't seem to do anything for me but I read a comment that deleting some dubious looking files in "/Library/Application Support/App Store" seemed to do the trick. I moved these 3 files to a temporary directory and rebooted. At last! The problem seems to have been fixed. 2 of the files were recreated, the 3rd (utd.plist) wasn't. I will leave it for a few days before declaring success.
Best Answer
I was having the same problem with the Xcode 6.0.1 update continually showing up in the App Store. I applied the same update several times during my troubleshooting, even though during the process I kept deleting Xcode from my hard drive, I have no need for it any more. I didn't have more than one copy of Xcode on my drive, one possible reason for this issue.
I just solved my problem. I had disabled Spotlight indexing a while back, on the advice of a web page I had seen, because it was using too much CPU and I didn't believe I really needed it. What I didn't know was that the App Store depends on the Spotlight indexes to determine whether you have an app installed; it was looking at a stale index.
I just re-enabled indexing ("sudo mdutil -i on /"), and as soon as Spotlight actually started re-indexing, the App Store decided I didn't have any updates to be applied for Xcode.