Using the scroll wheel to zoom in either direction will sometimes cause fast zooming which does not stop when the scroll wheel is stopped or reversed. Sometimes esc or RMB will stop it after a while.
This has been happening this week with increasiing frequency and is now up to about once every half hour.
When this happens, scroll zoom works fine if I launch Sketchup but when flipping back to Rhino the issue is still there. It happens with two of my three mice. Closing and restarting Rhino will usually fix it.