Seriously, though. I have read about several people having the lockup issue. In my case, I was able to identify something that, when undone, removes the lockup problem. Many people, when they get a new camera, probably microadjust at least one lens before trying a TC. They may think the particular TC simply does not work with that camera, never giving thought to the idea that AFMA (especially when it does not involve the lens used with the TC) could contribute to the lockup.
I don't know that it is necessary to have the adjusted lens on the camera when disabling AFMA. I don't recall whether I've had success when starting with another lens. I do know that with the 40mm on, it is necessary to take a shot after changing the setting. I don't know why, but it seems to "establish" the setting change somehow. It is not intuitive that you would have to do more than disable AFMA. So, without my making my experience clear, someone needing a possible solution to the lockup problem might try simply disabling AFMA and have it fail.
Just trying to help.
Sounds odd, but entirely plausible. The 1D X initially had a firmware issue where the AFMA setting was not stored/recalled properly. I had the issue, others did not. Turned out it was linked to the setting for Orientation-Linked AF Point, when that setting was enabled (it's off by default), AFMA 'broke'.
The workaround you describe sounds like the issue is a firmware problem, but unfortunately for users of Kenko TC's, Canon has no obligation to identify and solve the problem (the opposite, in fact). So for people using the Kenko TC's and having lockups, this may be the only option. Thanks!