Actionbar border texture fading

[Tatsu]

I'm using an old texture pack from Santa UI Textures for my actionbars.

Problem is they keep reseting to default when I open spellbook or move spells/macros. I saw some people commenting on the same problem on various forums but with no answers.

Screens before
https://i.imgur.com/aQZsNOI.png

After moving a spell or opening spellbook (reverts to default borders)
https://i.imgur.com/PBgngrA.png

Afaik its the UI-Quickslot.blp controlling the actionbar borders. But maybe I am missing another texture file. I'm not sure.

Anyone know what could cause this or a possible fix?