I have same problem in new phone!
The phones always pressed H and L or star help with the application shortcuts automatically when I pressed optical trackpad down.
I decided to fix my cellphone in person because I used to fix blackberry 9900 and believe that i had a capable to finish it. I found that the optical trackpad cable is slightly damaged when I presseded the cable. This cable connected with the metal piece on the motherboard which causing a short circuit and it will type two word H and L by itself. Finally,I used a small sticker to protect the cable.
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