Language::listToText() uses for(;;) which assumes the index in a list starts at 0 and following keys are consecutive integers.

This assumption fails (and results in warnings with E_STRICT) when SpecialListGroupRights::formatPermissions() uses the key-preserving array_intersect() to create a subset of $allGroups.

Solutions include using array_values() (again) in SpecialListGroupRights::formatPermissions() or to change Language::listToText() so that it uses array_values() or foreach()

(I prefer the latter.)