Deathmatch PvP Arena Cannot Unbind Tab toggle scoreboard

I am able to bind to Tab to my skills, so I bound it to Specialty Meter. When I hit tab in 3v3 arena, it toggles the Scoreboard, even though that is my Specialty Meter key. There is no option to unbind toggle scoreboard or rebind it.

If this is the case, Tab should not be an eligible key for rebinding, or this should be fixed. Tab is located next to W and is ergonomically efficient. X causes severe RSI and carpal tunnel syndrome. Please fix this gamebreaking PvP bug.

Allow the Toggle PvP scoreboard to rebound, or make it a different bind, for example.