FPU handling got broken over half a year ago when I removed separate interrupt DLL and added support for DPMI32. Interrupt DLL made sure that builtin protected mode interrupt handlers saw regular IRET return record on stack. Current protected mode interrupt code does not provide an IRET record and real mode interrupt code never did provide it.
I'm currently working on a two part fix for FPU code:
1. Make sure that DOSRELAY called via RELAY_BuildCallFrame sees original stack and code pointers and can modify them.
2. Make FPU emulation use CS/IP instead of IRET record.
Both of these patches are about 10 lines of code so I guess I shall have it fixed within a week, assuming testing patches don't take up too much time.