Originally Posted by
cxwrench
Cassette spins when freewheeling, effectively spinning backwards. You don't have to back pedal to make this happen, it just spins faster when you do. Cassette ALSO spins freely when pedaling forwards, effectively no drive. Get it?
Ok, but I'm trying to picture what OP experienced when actually riding (forward) on a bike and chain is connected with a freewheel that isn't engaged. If the cassette is spinning forward when coasting then I'd think the chain would be dropped real quick, and to move forward it would have to fight the RD tension. If pedaling forward or just coasting, the cassette likewise can't spin in reverse as the chain (connected to the crank) wouldn't allow, And if pedaling backwards the cassette will spin at whatever speed you're pedaling backwards because the chain is pulling it.
I can imagine seeing the issue with bike on a stand and/or chain removed.