Putting this here so it doesn't get forgotten. Appearently replying to threads that get merged in the meanwhile causes some problems.
Steps to reproduce:
Needs further investigation, may depend which thread is being replied to and which one is merged. Info so far:
13:11 < RiverRat> reproduce (I think), click the quote button and start typing while an admin moves the thread and then click preview and it says something like (It's gone now): Can only comment on threads in the forums.
Wrong product - i suck.
Fixed in CVS. Needs testing. - Will close bug if test was successful.
Tested on ftest.