bug? Vendor Invoice update

[david <..hidden..>]

I'm doing something very naughty...  I've made some mistakes in vendor invoices 
and want to correct them (specifically, I entered purchases for incorrect service).

If I modify the service, then update, then post, I get a warning that I'm 
changing a record. If I proceed after the warning I get an error message thus:

DBD::Pg::st execute failed: ERROR: duplicate key value violates unique 
constraint "transactions_pkey"
Error!

INSERT INTO ap (id, vendor_id) VALUES (?, ?)
ERROR: duplicate key value violates unique constraint "transactions_pkey"


OK so far because I'm probably doing something that I shouldn't do, but then the 
record of the transaction completely disappears - both the original and the 
updated version.

If I'm not allowed to proceed, then surely the system should either not let me 
proceed after the warning, or else leave the original record intact?
I'm now concerned that there may be some mangled record in the database, 
although diligent searching hasn't turned anything up yet.



BTW, if I simply change the notes and re-post despite the warning, then the 
update is successful, which is a good thing in my view and I would like that to 
remain.


regards,

David