What it is, is the BOV spring pressure is set too high, or the vacuum signal to it, sucks (no pun intended.)
Either way, it's not healthy, by any means, especially for your turbo. What's happening, is, air is being forced backward when you close the throttle plate (and the bov isn't opening), causing the pressurized air to make its way back through the IC, and to the compressor housing, pushing the wheel (trying to) opposite of it's rotation..
Imagine the stress on the CHRA when the turbine side is still being turned the proper way, by exhaust gases, yet the compressor is trying to follow suit, but meets this backpressure resistance..
Fix it. Soon.