Bug with transaction numbering

When I enter an expense it suggests TRA-0001 as the transaction number. But this is already taken by a previous expense or income. I expected the system to take the next number available. This means I have to cancel what I am doing, look up the last transaction, remember the number and add one. I suspect the system might work but because I did a manual import from a spreadsheet - this has exposed a bug. Thoughts?

Chris