pl2303 lockups on rpi2

[bob prohaska]

I'm seeing lockups of two (out of four seemingly identical) P2303TA USB-serial
adapters on rpi2 at r 301978. A sample  console message is 

login: 

FreeBSD/arm (ns1.zefox.net) (ttyu0)

login: uplcom0: at uhub1, port 4, addr 5 (disconnected)
usbd_req_re_enumerate: addr=5, set address failed! (USB_ERR_IOERROR, ignored)
usbd_setup_device_desc: getting device descriptor at addr 5 failed, USB_ERR_IOERROR
usbd_req_re_enumerate: addr=5, set address failed! (USB_ERR_IOERROR, ignored)
usbd_setup_device_desc: getting device descriptor at addr 5 failed, USB_ERR_IOERROR

The device is stuck hard, even through unplug and replug. However, if it's plugged
into a Mac running Prolific's drivers it's recognized and will then work for a while,
sometimes days, on FreeBSD.

The problem seems to move with the adapter from one RPI2 to the next, which suggests
a bad adapter, but I'm wondering if it might also be a driver operating on the edge.

I can find no evidence of difference between the four adapters: The chip packages 
look the same, all the numbers match and the soldering looks good.

I've been hesitant to take a refund up to now, but unless somebody thinks there's
a driver issue on the FreeBSD side perhaps I should change my tune....

Thanks for reading and any thoughts,

bob prohaska