Today I encountered a problem where if I open the normal patcher, it will actually open the PBE patcher instead. I have tried numerous things to fix this, including restarting the computer and opening it from inside the installation folder.
Note that when the league of legends logo appears, it flickers 3 to 4 times before the patcher comes up. If I open the PBE patcher directly, it won't flicker at all.
Also, this might actually be a problem on my side, as I am no longer admin. In that case I would love to know how I might be able to fix this.