I believe the issue is that the lens mount is not perfectly flat. This could be for two reasons - either some washers missing under the lens mount or, a warped body. By tightening the lens, uneven force is applied to its helicoid and thus the focusing action becomes 'sticky'. The only way to check this exactly, would be using a depth measuring micrometer (body lens mount vis-a-vis pressure plate) or a collimator.
I have had a similar issue with a 1.5/50mm Summarit and it only happened on one body, when the lens was tight in the mount. I paid no attention to it, as I had a few other bodies where the problem was not present.....