I only use the Celestron focuser with the linear method of my Celestron 8HD Edge. I'm not sure that I would describe it as an issue with the mechanics... the current process just doesn't give the focuser time to complete the "out" movement before it issues an "in" command. It may be working fine and I'm simply experiencing what Doug is describing. However, when I'm sitting at the scope it sounds like it starts reversing before it finishes the out movement.
This is one of those situations where I would think it wouldn't hurt to have a very short (1 sec) pause between commands.
BTW... I'm not fond of the Celestron focuser. I sometimes experience connection issues with INDI... seems unstable. I've ordered an ZWO EAF to replace it on the 8HD Edge, but have been waiting several weeks for the back order to clear.
The ZWO EAF on my refractor works perfectly with the polynomial process.