Using the CVS head, but this has happened for awhile both under OS X 10.4 and 10.5
Open the transcript editor and a long transcript. If you delete lines from the transcript the scroll bars are not rescaled (minor cosmetic issue) but it means that the length of the text is not updated.
So after deleting a bunch of lines if you scroll to the end of the file, the transcript editor locks up and you have to force quit.
The work around at the moment, is to enter something in the search box and then click the x to cancel. This forces the scroll bars to rescale and all is well again as the size of the file is synchronized with the window.