There are three problems fixed with the V1.6.4 software/firmware release:
1) In some systems, the autotuner doesn't detect the "wobble" correctly and as such doesn't tune the algorithm to compensate.
2) There was a combination in the configuration that could cause the machine to slow down unexpectedly. This was fixed on most systems with V1.6.3.
3) Interpolations on linked axis (where two axis act as one) would unlink the axis on circular interpolations.
**As for when V1.6.4 is released, I don't want to put a date on it, but it is very close. We are running very behind and playing catchup (No denying that fact)
V1.6.4 got caught between major enhancements, bug fixes, and bad timing. Made the update WAY too big.
Don't plan on making that mistake again (hindsight being what it is ). We prefer small, quick changes.