Pistons have the ID 33:7 and not 33?

Pistons seem to (sometimes?) have the ID 33:7, and sticky pistons have 29:7. It's annoying on my server because I have a shop plugin that sells things based off of their ID, and people are sometimes not able to sell them when they have :7.

This also happens with leaves blocks.

EDIT:
In the screenshots I uploaded, I just dragged the pistons from the creative inventory to the hot bar.