Isn't that a memory mapped FPU, accessed at 0xfffa40?
That won't be reported as 68881, at least not in the cookie.
BTW, while trying out a new version of the detection code i found another problem. When i set the CPU/FPU in Hatari to 68040, i get a NULL frame instead of a IDLE frame. Looks like the fnop is not executed at all (fpu_state in cpu/fpp.c is still 0 when the fsave is executed). When i do something like fmove fp0,fp0 before the fsave, everythng is fine. I haven't tried the old UAE version, though.