I have this problem with some items like Stones, ore, metal frags, wood. I have changed stack to 5000 or 10000, but it resets after a while to 1000. Same has been for 5.56 ammo where I choose 256. It changed back to 128. Now I have 512 and it looks stable, for now. I have no other stack size plugin installed.  Kind regards Ragtime

Must be something wrong with latest optional update I assume. Go back one update 

Thanks! I try that and see how it works. Kind regards Ragtime

I've pulled the optional update 1.4.3 

Please use 1.4.2 should work fine

It seems like working now. Not sure why it suddenly desided to keep it sizes, but great :)