With a MPS setting of 1.4 USB doesn't work on me; it timeouts,
constantly.  With MPS setting of 1.1 everything is OK.

a dirty diff of lspci -vvvxx gives

     62c62
     <       Interrupt: pin D routed to IRQ 5
     ---
     >       Interrupt: pin D routed to IRQ 19
     77c77
     <       Interrupt: pin D routed to IRQ 5
     ---
     >       Interrupt: pin D routed to IRQ 19
     103c103
     <       Interrupt: pin A routed to IRQ 11
     ---
     >       Interrupt: pin A routed to IRQ 18
     124c124
     <       Interrupt: pin A routed to IRQ 5
     ---
     >       Interrupt: pin A routed to IRQ 19
     140c140
     <       Interrupt: pin A routed to IRQ 10
     ---
     >       Interrupt: pin A routed to IRQ 16
     157c157
     <       Interrupt: pin A routed to IRQ 12
     ---
     >       Interrupt: pin A routed to IRQ 17
     186c186
     <       Interrupt: pin A routed to IRQ 10
     ---
     >       Interrupt: pin A routed to IRQ 16

(I've attached both lspci -vvvxx's, so you can diff -u that if
you want).

My question(s) is(are) is this a known bug, is this correct
behaviour, am I missing something, and why is USB the only
subsystem affected.

Phew.

-- 
John Lenton (john@grulic.org.ar) -- Random fortune:
Se Deus é amor e o amor é cego, Ray Charles é Deus?