I have spoken with her before about them.
Here is where I stand about things like this - if you have had some tests run, and there are no symptoms, no clinical signs that cause concern to medical professionals (change in size, dark pigment, etc) and no trouble from it, I don't worry about it. Just like with people, some variation in physical features, while not common, is not abnormal. People might have birthmarks, skin tags, moles, folds in the ears, pronated feet/ankles, etc. These are differences we will notice when looking at them, but they aren't health risks (well, the pronated ankles are, but you get my point).
So, since there is nothing actually wrong with the glider(no symptoms that cause concern), I would just say it gives him character and go on enjoying the heck out of 'em.