Forwarding a bug report from mediawiki-l:
[MediaWiki-l] Obvious bug in maintenance/Maintenance.php since 1.31
REL 1_31 introduced 'mwdebug' option in Maintenance.php (in the code it
mentions that --debug was taken by some script). The code incorrectly adds
the option via addOption() by setting the 4th argument to true (takes an
argument). This should be false. At least, the rest of the code is clear,
and so is the intent: there is no option to be taken.