I just noticed while customizing my Spooky Skimmer Mount, that the reins on the spooky skin are bugged. They behave like rubber and seem to be attached to parts of the mount's body, which might be the reason why they are being stretched like that.
This issue does not exist on the orginal mount skin.
Since the Skimmer skin is one of the main reasons I even got the mount pack, I hope there will be a fix for that, especially since the free skin coming with the expansion does not show that behaviour.
The body part the rein texture is attached to is the pipe-like organ the skimmer uses to blow air out of (sorry, no idea what would be a fitting English term for that). Here's a video showing the issue: