Project key in post function parameter

I have created my own workflow post function class that triggers on create issue step, however there is one thing I noticed. When I create an issue and the postfunction receives transientVars parameter in “execute” method there is usually property called “pkey”, which obviously holds the project key. However, when the issue is cloned the “pkey” is missing. Is this some sort of inconsistency? is this the same for Jira 9 DC versions? will it be changed in the future?