It's more likely that the BT and wifi don't have specific co-existence support, and BT is trampling over wifi or vice-versa. BT hops all over the 2.4GHz band, including all over the frequencies that wifi uses...
Very very interesting. Do you think that perhaps it's this very coexistence support that's making the two devices swap frequencies back and forth?
Wouldn't there also be glitches with the download if they were trampling on each other. Does the download loose speed at the same time as the mouse acts up?
Is BT a polled service like s-bus? Maybe the mouse is being swamped by other signals? What it can't hear it can't respond to.