[Boatanchors] General question...frequency shift with RF gain

[John Saxon]

On the Hallicrafters list a fellow reported a receiver that shifted frequency with RF gain adjustments.  Several folks responded that they had had a similar experience. I am having the same issue with a National NC-101X.  Just out of curiosity:  Is a frequency shift with RF gain adjustment common?  uncommon?  in-between?
Just wondering...
--JohnK5ENQ