(first message should come up as by spiliot, 6th page)
I blind edited the int handler to do something with the interrupt instead of just exiting. This now works in my case without any implications.
The first time I send something to /dev/usb/lp0 (debug enabled) I get a
usblp0: nonzero read bulk status received: -5
which probably explains why the dwc_otg driver was entering the INT loop in the first place, but I lack the knowledge to pursue this further.