Apologies if this has been asked somewhere. I tried searching for a solution to this for a while to no avail.
When I press CMD + TAB on my Macbook Pro (Yosemite 10.10.3) to open the application switcher, normal behavior allows you to release the TAB key and hold CMD to keep the switcher window open, then tap TAB as necessary to reach the desired application. Instead, my machine continues cycling to whatever application is on the far right, as if I were also holding down the TAB key.
I haven't noticed any odd behavior anywhere else. I tried repairing my disk (which did need to be repaired), but now everything says OK and the behavior still persists.
Let me know if any other information would be applicable. Thanks.