The find tool doesn't work properly when the [Account] [Matches no account] condition is selected.

Reproduce it this way:
• gnucash --nofile
• file -> New -> New Account Page
• create 3 accounts a, b and c with default settings
• enter 3 txns with any value, and with accounts respectively: a->b, a->c, b->c
• edit - find  [Account] [matches no account] [selected accounts] doesn't work properly

If you select account a, you expect to get all the txn that doesn't involve account a, i.e. only the b->c txn. On the contrary, you get all the 3 txns.

If you select accounts a and b you shouldn't get any txn, because the 3 txn involve either a or b. But unfortunatly you get 2 txns: a->c and b->c

Apparently the bug is easy to solve: it should be a matter of changing a OR clause with an AND one.