The SEE_PIXELs flag overrides the effect of that TILE_BOUND has on the visibility of an object.
Initially I wasn't sure if this was 'a bug' or intended behavior, but recently someone linked me the original feature request in which lummox said http://www.byond.com/forum/?post=2054167#comment19080430
It doesn't. An object with TILE_BOUND will either be visible or invisible depending on whether its tile is obscured or not.
The tilebound objects do not seem to respect invisibility when obscured if a user has SEE_PIXELS.
Numbered Steps to Reproduce Problem:
1. Pixel shift an atom/movable to another tile
2. Obscure the original tile it is on while making the tile it is pixel shifted onto visible
3. Add SEE_PIXELs flag, object becomes visible
Code Snippet (if applicable) to Reproduce Problem:
http://puu.sh/pJf9o/fb4af90f50.rar
A test case, all the objs in this test have pixel_x = -64, shifting them two tiles to the left. When on the left side of the wall you cant see them, but with the SEE_PIXELS flag you can see them again.
Expected Results:
Pixel shifting an object from an obscured tile should keep the object obscured with SEE_PIXELS or without it.
Actual Results:
SEE_PIXELS overrides the base behavior of TILE_BOUND entirely
Workarounds:
None known
I don't think this is fixable, or truly a bug as such. The map is drawing as intended: Objects on the hidden tile that have pixel shifts are meant to be drawn, so that they can be properly covered up by blackness when appropriate. It just happens that in this case there's no blackness to cover the object.