Many thanks.
The money has appeared in the destination account, so obviously the transaction did go through the first time, hence why subsequent sends failed because my balance wasn't sufficient. The bug must be in putting transactions into the history ....
thx again for letting me know, very worrying for a bit!
No problemo... I was in the area because I had a couple of transactions that just either got confirmed and never showed up in my client or were stuck.
https://bitcointalk.org/index.php?topic=307079.msg3393444#new