the mstatus register does not implement the FS and VS functionality

[EAlexJ]

In the current implementation the mstatus writes and reads are masked, based on the privilege wrapper used. This means writes to most of the mstatus bits never appear, as there is no consideration wrt the actual underlying ISA.
This causes confusion when debugging.

On top of that, Instructions using the F and V registers are always legal, regardless off the setting of the bits in mstatus.