I have noticed it very occasionally with .177 but not with .20 or .22. I suppose it is because the seventeen .177 pellets are crammed in a bit more making perfect rotation and probe alignment that bit more sensitive.
The latest edition of the Rapid has a scalloped loading port a la MFR to enable easy single shot loading. Arguably it is a major improvement in the design of the Rapid receiver which doesn't get as much attention as it deserves.
Single loading is more difficult with older Rapids but not impossible unless you have very fat fingers indeed.