Tabbing out and loosing the ability to enter any sort of input from the keyboard

I was playing a game as DJ Sona, tabbed out to open an important email from my employer while I was dead tabbed back in to find I could not cast any spells, use chat, or enter any hotkeys for emotes, Sona's Song change, or Mastery. Basically all keyboard input was not being received. I could still Right click and move.

Exiting game and returning did not help Turning off the game and logging back in did not help, as I could not type my password for log in Only Shutdown and restart of the computer helped.

Further info about the incident: Browser tabbed to - Chrome Email Client Used - Yahoo Mail OS - Windows 8

P.S. I got a leaver warning for software malfunctions outside of my control, may I please have it removed off my record. I understand if you decide not to.