Jared,
I think this describes the behavior of my iOptron CEM60. I do not know exactly how iOptron handles a Sync command that comes through the ASCOM driver, but I do know they say you must delete the mount alignment model when using an external program which has its own pointing model. I assume plate solving must fall into this category.
In my experience with the model in the hand controller active the mount was exactly off by the same number of pixels on everyone one of ten attempts (>250 pixels). After I deleted the model using the hand-controller the mount falls within 2-5 pixels on the first iteration. Therefore, it is not a mechanical issue with the mount, but a software issue in the ASCOM driver or hand-controller firmware that is causing this behavior on my iOptron mount. Therefore, I agree with Jared that the issue needs to be addressed by the mount manufacturer or ASCOM developer.
Fred