In PluginInstaller.php there is
$constraint = new VersionConstraint($version, $operator);
on line 168 BUT in the VersionConstraint class in Composer the args are the other way round see https://github.com/composer/composer/blob/master/src/Composer/Package/LinkCo nstraint/VersionConstraint.php#L60
I found this recent change which might explain why code which was silently failing before does not any more https://github.com/composer/composer/commit/8dd110e0a986036064edc4d259d8b5d6...