Diagnosis
This is almost always a sticky button or a short in the keypad. Spills, dust, or just a defective membrane under the buttons can cause phantom presses.
How to Fix It
Unplug the desk. Carefully clean around all the buttons on the handset with a cotton swab dipped in isopropyl alcohol (90% or higher). Press each button multiple times while it's wet to work the cleaner in, then let it fully dry for 10 minutes.
If That Didn't Work
The keypad cable might be partially shorting. Follow the thin cable from the keypad to the control box, unplug it, inspect for damage, and firmly re-seat it. If the problem persists, the keypad needs replacement.
Heads Up
Don't use compressed air to clean the keypad. It can force debris further inside. And if you see liquid damage, cleaning likely won't fix it—you'll need a new handset.