No, it really definitly is running on 20 Mhz,

Fuse PLLDIV_5_1L provides internal 4MHz which is used to to drive the 96Mhz internal PLL which gets divided to 48Mhz for USB via _CPUDIV_OSC1_PLL2_1L & _USBDIV_2_1L. Fuse _FOSC_HSPLL_HS_1H should select the right frequency for the MCU promary clock.
DS39632E-page 31 & schema on DS39632E-page 24

Have no PBP at home, only able to access the source. If you have access to the PBP libs and lookup the PBP config fuses, it should show that a 20 MHz OSC could work.

USB communication is no problem, the 2400 baud on 2550 is seen on oscilloscope IIRC. (now at home - at friday night or saturday able to clock it again).

Thanks for the fast reply.