I confirm this issue, which has been reproduced consistently with all SVN versions of CB over the past few weeks, including the latest svn5109.
The bug strikes me as probably more scintilla-related than strictly CB code-related; but this is a wild guess.
As I've been developing extensively on CB/Linux (Ubuntu 8.04) with CB, I also confirm that the bug is a very annoying one.
So more details:
Cursor shift always happens rightward, and may be up to 3 character positions ahead of 'actual' writing cursor. Normal position is retrieved by pressing 1 to 3 times (depending) on the "DEL" key, which seemingly eats up "dummy junk" characters that are not displayed on screen. I've pinpointed no particular context that sets the bug showing up: it's seemingly haphazard.
Best, Fab