Non-Square Textures - Weird Brush Behaviour

Hi everyone.
I have an issue with painting non-square textures.

My setup:
I layed out a UV shell across 1 V-tile and 4 U-tiles in Maya. So, a 1:4 ratio e.g. 4096 x 1024
Then scaled it along the U axis to fit the 1:1 UV space and exported.
I bake the map with a res of 4096x1024 and set the Texture Set Setings to 4096x1024 resolution aswell, so the baked map displays correctly.

Now for the issue.
When i paint on a layer or layermask, it will paint a distorted stroke of whatever brush i use.. Pretty much a 1:4 ratio stroke. It becomes very inacurate and unpredictable.
I can solve this by setting the Texture Set Settings to a 1:1 ratio e.g. 4096x4096.
This will distort the baked map itself though and once i set it back to 4096x1024, all strokes are messed up heavily.

So, what am i overlooking here ?