Thanks for this - it's a bug in Q2A which shows up under certain versions/configurations of MySQL which don't use an implicit default value for a column. You can fix it by making the following changes in qa-db-votes.php:
In function qa_db_uservote_set(...), change:
'INSERT INTO ^uservotes (postid, userid, vote) VALUES (#, #, #) ON DUPLICATE KEY UPDATE vote=#',
... to ...
'INSERT INTO ^uservotes (postid, userid, vote, flag) VALUES (#, #, #, 0) ON DUPLICATE KEY UPDATE vote=#',
Then in function qa_db_userflag_set(...) change:
'INSERT INTO ^uservotes (postid, userid, flag) VALUES (#, #, #) ON DUPLICATE KEY UPDATE flag=#',
... to ...
'INSERT INTO ^uservotes (postid, userid, vote, flag) VALUES (#, #, 0, #) ON DUPLICATE KEY UPDATE flag=#',
These fixes will be rolled into the 1.4.1 release.