El Capitan intermittent USB multi-media

I use a pair of Bowers & Wilkins MM-1 speakers which have worked flawlessly through several revisions of OSX.

Having just upgraded to El Capitan I now find that my Macbook Pro will often fail to recognise them. I have my speakers plugged into the USB port on a Thunderbolt display and I find that having disconnected my Macbook from the display and then returning later, it will not then detect the speakers.

A full OSX reboot solves the problem every time. If I boot with the Macbook either connected to or disconnected from the Thunderbolt and then hook everything up it will then happily find and work with the MM-1 without any issues. It seems the act of disconnecting from the Thunderbolt is causing the issue.

I've also noticed that video devices (such as the Thunderbolt camera) are also not being detected properly after a disconnect from the Thunderbolt, nor the in-built Thunderbolt audio either - all of which presumably hang off the internal USB bus.

Never seen this behaviour before and it is coincident with the El Capitan upgrade. The fault is very repeatable. A reboot always cures it. Same thing occurs if I use other Thunderbolt displays. Got to be an El Capitan bug surely?

Anyone else seeing anything similar, perhaps with other types of audio or multi-media kit?