https://www.phpbb.com/community/posting.php?mode=reply&f=46&t=2261151 can be reproduced by me: submitting a value too large will result in an error page that gives me the full information although I don't have administrator permissions and DEBUG might also not be set for phpbb.com's phpBB.

Trying to reproduce this on a vanilla 3.0.12 installation brings back the screen I've expected: only the textual database error without showing any SQL or even a PHP backtrace.