Copying and pasting text only pastes a hyphen character

You should not hit the clipboard buffer limit in normal use, it is far bigger than a “block of text”. Depending on where you copy from, the source application might be transforming the buffer before storing it. Especially some websites have scripts for these kinds of interceptions in an attempt to prevent large-scale copying of copyrighted information – in these cases you can often work around using the Edit > Copy menu item instead of the Cmd-C shortcut, for example. Other applications might change the clipboard format after reaching a certain size, and might then have a bug when generating e.g. a Rich Text buffer versus a Plain Text buffer. Another thing you could try is pasting with the Paste and Match Style option, by choosing it from the Edit menu or pressing Ctrl-Shift-Cmd-V.