u-boot on RZ A1/M hangs in "usb start"

The “usb start” command always hangs in "scanning bus 0 for devices..." , if a certain wifi dongle is plugged in.   Any thoughts on what could be causing this? Why is the timeout not happening?

 

=> usb start
starting USB...
USB0:   scanning bus 0 for devices...

 

This is not a total hang or crash, because if I’m doing it interactively in u-boot, and hit Ctrl-C while its in thus hung state, the “usb start” command exits and reports "Cannot read...."

 

=> usb start
starting USB...
USB0:   scanning bus 0 for devices... usb_new_device: Cannot read configuration, skipping device 0cf3:9378
1 USB Device(s) found
       scanning usb for storage devices... 0 Storage Device(s) found

 

 This does not happen w/ all WiFi dongles that I have tried, but one dongle does report some error (but no hang).

 

=> usb start
starting USB...
USB0:   scanning bus 0 for devices... USB EP descriptor overflowed buffer!
2 USB Device(s) found
       scanning usb for storage devices... 0 Storage Device(s) found