There is a difference in filtering behaviour for depexts for portable vs non-portable lock directories.
For instance, when an undefined variable occurs in a filter in a depext, non-portable lock directories will filter away the depext whereas portable lock directories will keep it.
We should investigate what exactly the differences between the two methods are, what behaviour makes sense to keep and what behaviours should be changed.
One such example of this behaviour coming up in practice occurs in #13674 (comment)
There is a difference in filtering behaviour for depexts for portable vs non-portable lock directories.
For instance, when an undefined variable occurs in a filter in a depext, non-portable lock directories will filter away the depext whereas portable lock directories will keep it.
We should investigate what exactly the differences between the two methods are, what behaviour makes sense to keep and what behaviours should be changed.
One such example of this behaviour coming up in practice occurs in #13674 (comment)