I'm glad that the situation is getting better.
I have a desire to Porteus MATE
normally (default)
shows the partitions in file manager
as in other versions of Porteus.
Like Porteus-KDE, XFCE, LXDE, RazorQT etc.
The existing situation (I do not see the partitions in the Porteus MATE file manager)

Simply as Linux Mint MATE (normally shows the partitions in MATE file manager)

Probably not easy to find a solution.
I hope and waiting for the best solution
brokenman please make Porteus-MATE.iso
with possibility that
normally (default)
shows the partitions in MATE file manager
I m waiting
to try / test Porteus-MATE.iso in live mode with this possibility.
All the best.