Hi Nick, sorry for the serial posting.
My partner just came home & she said that there are problems mixing pre-1.5 and post-1.5 clients because the former won't create information that the latter require when merging. Where she works had problems with this until they understood the cause. This is most likely why the original branch you created with a 1.4 client was corrupted when I merged it with a 1.5 client. The manual specifically recommends against mixing client versions and recommends upgrading to 1.5.
Cheers Lex