Certain key combinations (involving CMD) don't work

My left command key is not working for certain key combinations, but it works fine by itself, and in some other combinations. e.g.

Fails:

• left-cmd + tab (switch apps)
• left-cmd + w (close window/tab)

Succeeds:

• left-cmd + r (refresh)
• left-cmd + s (save)
• left-cmd + /* anything else I’ve tried */

Also Succeeds:

• right-cmd + tab
• right-cmd + w
• right-cmd + /* anything else I’ve tried */

I’ve tried:

• zap PRAM: still fails
• restart: fails
• safe mode: still fails
• pulling my hair out:
  still fails

Could this be a keyboard hardward problem?