generated Blender cubemap with unwanted "motion blur"

We’ve been rendering a lot of 360 spherical environments into the Blender cubemap format and haven’t had any problems. With the last update to Blender 2.77 we noticed a motion blur on the rendered cubemap. Looking at the top and bottom tile you clearly see a twirl, like the background or the camera is rotating counter-clockwise.

This is the same scene, we always used to render these cubemaps and neither there is a rotation on the camera nor the background. The source image is 8000x4000 and as sharp as it is supposed to be. Does anyone have a clue what’s going on?
Thanks in advance.

We figured out that the image filtering is causing the problem. Turning of anti-aliasing removes this blur but the image will be sampled with nearest pixels then. Changing filter modes instead doesn’t work at all. I’m not sure if we miss something or if this might be a bug in the current release 2.77a because it worked before.