Am I seeing the effects of diffraction?

LH all things being equal maybe yes. But if things are not equal then maybe no.

The reason why is the depth of field. I do some macro which is greater than 1:1 using tubes. The depth of field even at f8 f12 or f22 is so shallow that this is a possibility. Looking at your two images I would say this is what has happened. You have by changing the aperture set the lens a millimeter or two closer to the pen. The focus in the f22 shot appears to be further away than in the first image. If you look at the pen further down in the second the same blur is not happening as on the ball. the diffraction would be more prominent over the image as a whole.

I am presuming you are seeing what maybe diffraction on the ball of the pen in the second. Well you would not see it only on the ball. This suggests you have moved the camera focus point for the second image and the ball is simply out of focus or within the MFD.

Having said that yes there is diffraction over the whole image and if that is what you are referring too then yes.

Dont under estimate the shallow depth of field in Macro.

LH looking again I think it maybe a bit of both. slightly different focus point and diffraction. It is not always the f stop that is paramount, quality of lens can help for diffraction.