Malzahar's ult and Leona's Q...
So i have encountered two bugs within the past year of league that have really come to light the more I've matured as a player. As i love these champions I think that these bugs essentually overpower or weaken their gameplay. (Sorry about the fluff above)
First off with Malzahar's ult. When using e->w->r sometimes r refuses to suppress a target and they are still able to use abilities and aa while he is ulting.
With Leona's Q I realized that her q was proc'ing her passive which should not be possible as her passive clearly states that it can only be proc'd by allied champions and not leona herself. As well her w and e passive only proc on other champions and not Leona.
I have had these happen quite a bit within the past year as these are two of my favorite champions but I have only really noticed them recently.