I've built roofs on buildings using stairs, under the roof I have placed upside down stairs to complete the desire look. When two walls meet I have an upside down corner stairs.

This is were the problem is. Although I can get the desired inner corner when placing, after I leave and return (some times switching computers) the inner corner now turns to an outer corner. This also happens when you have a outer corner, it changes the direction it's facing.

There are no issues with stairs right side up, Just upside down.