I thought the Frank'n'Mouse port on my PC20-III is broken until recently, when I started it without HDD connected... and it detected the mouse port 😳

Any idea what can cause such behaviour?

BIOS version is 4.38 and motherboard revision is 6.2A

Motherboard is very nice - It was removed from the case only when I was cleaning it and there were no battery leak dammage.

JP206 and 207 jumpers are on.