For some reason the game only allows to map 8 way PoV hats as axles and not as buttons which in my experience is rather unusual.

I am using a CH Products Combatstick and Pro Throttle USB, I have no other issues and am greatly enjoying your game with the expansion, I could probably get around it by using the CH Control Manager mapper but if it's not specific to CH Products hardware the issue might be problematic for sets that have less comprehensive software suites.

In my experience Windows detects 8-way hats (AKA PoV hats) as if they were a 8 direction d-pad (technically is vice-versa but that's beside the point) while a normal 4 way hat is detected as 4 separate buttons and those seem to work fine, probably the plug in you are using is doing something similar and either it doesn't allow for a d-pad direction to be mapped as a button or it treats a d-pad like it was an analog stick and there is both the possibility that the plug in may be hardwired that way or that there is some option to not consider PoV or 8-way or D-pads as such.