Descriptive Problem Summary:
Overlay with alpha mask that has an y offset makes the visible overlay transparent to the mouse.

Numbered Steps to Reproduce Problem:
1. Create an obj with an icon that has transparent parts
2. Cover the transparent part with an overlay that has a mask with an offset
3. Observe the masked overlay be transparent to the mouse

Code Snippet (if applicable) to Reproduce Problem:
https://cdn.discordapp.com/attachments/725458744711839873/ 1296529439727026206/filtermouse.zip?ex=6717e4a2&is=67169322& hm=51a957ef6b17b92ba4e8f8216971766a4a21f8f010add8dabebcaa430 f8f5ace&

Expected Results:
Mouse detects the obj where the overlay is visible.

Actual Results:
Visible overlay is ignored by the mouse. Sometimes the overlay is detected by the mouse at the wrong spot.

Does the problem occur:
The problem seems to consistently happen at offset y=4 or larger. It does not happen with x offsets. After further testing it looks like the visible overlay is detected at the original position where it would be without the mask offset. I am not 100% sure though.

When does the problem NOT occur?
Seems to occur every time there is a y offset to a varying degree. Depends how far the offset mask is from its original spot.

Did the problem NOT occur in any earlier versions? If so, what was the last version that worked? (Visit http://www.byond.com/download/build to download old versions for testing.)
No known last version where this didn't occur.

Workarounds:
No workarounds I could find.