Using the left stick moves the right stick too. Waa?

After about a couple months of use my Wii U Pro controller started having this problem where if I press the left analog stick to the left it acts like the right stick is simultaneously being pressed down. Similarly, pressing the left stick to the right also presses the the right stick up. Moving the right stick does not produce the opposite effect.

I've tried recalibration the sticks but this feels more like a defect than a simple calibration issue.

Example:

When playing StarFox Zero (co-op mode) if I bank to the left (L-Stick Left) it also puts on the breaks (R-Stick Down)