This is a follow-up with pictures included. My mahonia beleai(?)had two...
We are unable to accurately diagnose the problem with your mahonia, but we will circulate your photos through the diagnostic community and hopefully come up with the correct diagnosis.
In the meantime, the devices on the underside of the leaves resemble leaf galls. You should cut into two or three of them and look for some evidence of small insects.
It is also likely that this condition does not suggest a continuing problem, since apparently only a few leaves were affected.
We shared your photos with the Professor in charge of our diagnostic laboratory. She recognized the condition as edema. This malady usually occurs during periods of very wet weather or heavily irrigated plants. This is not a pathogenic condition and should not re-occur under normal conditions. No treatment is necessary.