When casting a summon spell the game recognizes the effect it puts on you as negative. As such, if you have an absorb magic effect up, then you'll have a chance to absorb your own conjuration spell. This is a bug that I find to be both a blessing and a curse. It is a blessing in the fact that the game recognizes you failed the spell so it refunds you the cost of the spell, but it also recognizes that you absorbed the spell so there is a chance, with every cast, that you can get additional mana. I've gotten out of many close fights due to being able to replenish my mana pool from my failed conjurations. But it is a curse in the fact that sometimes I just want to summon my [censored] atronach and have to spend 2 minutes running around dodging enemies while my summon spell fails 20 times in a row. Not to mention the fact that the atronach stone also interferes with many quests such as the Mage's guild quest where one of the apprentices turns you into a variety of animal.
This is a bug I've not seen anyone talk about because I really don't think many people are aware of it. As such, I worry that Bethesda will not get around to fixing it anytime soon. I like summon spells. I like the effect of the atronach stone. It annoys me that I can't have both at the same time.