A few things to check:
1) That you're using the correct command-line developer tools. (newer versions of Xcode 6.2+ rely on these for things like SourceKit etc..)
You can check this by running
xcode-select -p in terminal, and you should get back something to the tune of
/Applications/Xcode.app/Contents/Developer or the path to whichever beta you're using i.e.
2) Don't rename the beta-s i.e. '/Applications/Xcode-beta.app' to '/Applications/Xcode-6.2-beta4.app'. Things go awry with this!
3) Is your pboard working in general?
Drop to terminal and:
should come back with something such as:
504 367 1 0 2:20pm ?? 0:00.01 /usr/sbin/pboard
if it doesn't, double confirm that it's set up to be launched properly by:
launchctl list | grep pboard
this should come back with something like:
367 0 com.apple.pboard
Note the 367 shown in both for the PID. This basically indicates that my pboard is running fine...
If you get something else try:
and you should get something like:
4) When you paste into Xcode, and you get the spaces (i.e. missing characters), when immediately save the document, is the text there after restarting Xcode and reloading the project?
5) If you open Console in (Applications/Utilities/) do you see anything specific flashing up when you paste? i.e. any Xcode, DVT, SourceKit, Pboard etc... assertion errors etc..
- try pasting whilst console is open so you can see this.
- (the above tags I listed should be good filter words for console)
Let us know if this helps :)