Using for loop to set pinMode
Re  “Am I doing something wrong?”, yes :)

The sizeof(allOutputPins) expression returns the size of allOutputPins[] in terms of bytes, so is 24 because the array contains 12 two-byte integers.  The loop's last 12 pinMode() calls will be garbage.

Among other ways of fixing the problem, you could change the expression to sizeof(allOutputPins)/sizeof(int) [which has the same value, 12, as (sizeof allOutputPins)/sizeof(int); eg see the syntax entries for the sizeof operator at cppreference.com] or you could change the base type of the array to byte or uint8_t.