Stack Sizes can double ...

It's sporadic and has done this for days, but just now had time to enter a support ticket for it. Every now seems stack sizes double, for one slot and then goes back to normal. 

Example: 2x Server. Stack sizes for wood are 2000 .... player can be out chopping down trees and every once in awhile he gets 4000 in a single stack. This can and has happened multiple times to a player where he's had mostly 2000 stacks as he should, but then gets random 4000 stack sizes. This has happened to other items in-game as well, I am just using wood as the example.

Is this a known issue?

I am not aware of this issue, do you have any other plugins installed that might change stacking?