Hi Andrew,
I have an RST-135 and I'm the exact same problem you're seeing even with the latest release of Stellarmate. Running the mount with Windows / ASCOM the mount works without a hitch. I've also heard it works fine with the ZWO ASIair Pro and I'll be testing that shortly. At this time I can't recommend Stellarmate and the Rainbow mounts as a working combination. Hopefully, it'll get fixed soon.

Bill Clugston

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