Descriptive Problem Summary:
When pressing shift+leftarrow to nudge the active object to the left, it both nudges it by subtracting from step_x and pixel_x at the same time, moving it two pixels. None of the other directions have this issue, and nudge only with pixel_x and pixel_y (and pixel_w and pixel_z for up and down).

This ONLY applies to moving to the LEFT. No other direction has this issue.

Numbered Steps to Reproduce Problem:
Place an object/make an object active and then press shift+leftarrow. The object will move two pixels to the left instead of one, and decrement both step_x and pixel_x by one.

Alternatively, hold shift and press leftarrow rightarrow leftarrow rightarrow back and forth, and you'll notice the object just continues to slide to the left, since for each left movement it moves 2px and each right only moves 1px.

Expected Results:
Just pixel_x to be decremented (I have 'Nudge as pixels' enabled).

Actual Results:
Both step_x and pixel_x are decremented at the same time.

Does the problem occur:
Every time? Or how often? Every time.
In other games? Yes, in a new project the same issue happens.
In other user accounts? Unrelated to accounts, but yes.
On other computers? Yes, same issue. Had another user try.

When does the problem NOT occur? Never, that I can find.

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.)
Occurs in 512.1401
Occurs in 512.1393
Occurs in 511.1385

Workarounds:
None, have to just not nudge to the left ever if you don't want step_x to ruin sliding movement.