Items not Stacking

idkgiveme1

Reduce Fall Damage (34 days) - from purchasing

Reduce Fall Damage (25 days 1hour) - from ZP Crates


I believe these items should stack, they are exactly the same. I don't understand.
I have re-logged, I have refreshed the server, I've waited a day... and still hasn't stacked. Can somebody help me resolve this, as I'm loosing my days on the item.

Thanks