Mouse Button Key Bindings

When I play League I assign my hot keys differently from other players. Such as F for ignite, and flash for spacebar. (It's better like that, try it.). After I got a gaming mouse half a year ago, I've set my item #5 hotkey to MB4 (Mouse button 4), which is on the left side of the mouse along with MB5, where I set player attack move. I usually use MB5 for cs'ing and kiting because normal movement is easier to misclick. But for some reason lately, my MB4, and MB5 buttons are not working on League itself. I tested to see if my mouse was broken, but it's not, it's only happening on League. But when I set hotkeys in client, the MB's would work... Weird, but I need a solution because I'm so used to using MB5 and it's awkward and uncomfortable to switch back to my old style of playing. Also, MB3 (which is the scroll button) is my mastery emote, which seems to work fine???