Working through all the known bugs in preparation for Alpha 4, and just got back to this one, which is apparently not a bug.
I thought you were referring to standing on the stairs themselves (which could've been a transparency issue), but on closer inspection I realize you mean adjacent. This only happens when standing directly above and below, and is natural behavior for the engine because it's an emulated terminal that can only show one glyph in a cell at a time.
You
can see half of yourself when positioned to the left and right of an exit, but that's because each cell is actually composed of two smaller cells--the left and right halves--so it's still possible to draw one half or the other. Map cells cannot be divided vertically, so your top/bottom half will essentially disappear because that entire area belongs to the horizontal label lines themselves.
It's a side effect of the fact that I draw the map at regular "full square cell size" while most text is drawn in "half-width cells." For reference, I discuss the technique in
this blog post.
