Issues, Workarounds & Localization

Hello CCP,
after transferring some goods A from planet X to the hangar where already some A is stored the incoming A stacks with the present one but the new arriving amount is also places as a seperate stack. Now I wondered if amounts duplicated. When I try to move said stacks to my cargo I get an error message, which is fine, but it totally confuses me, that I see a stack which is not there apparently. The volume bar also indicates that something is there. So how I can I tell if something is really there?

This is hard to reproduce, on some custom offices this happens regularly and on others not.

Thanx in advance