When I had my phone, sent it back to be replaced due to a bad screen and running hot, it didn't do that for me. It did, however, have a weird glitch where it thought I was holding down the backspace even though I was typing. This happened about 3 times. Each time I would be typing in a rather fast pace and would mess up a letter so I would tap the backspace really quick and keep on typing; the phone thought otherwise and would begin to delete the majority of my message but would stop after about a second.
It could be another problem my phone was having. I'd keep running tests on your phone and making sure it's not human error before getting more concerned. But if you have already exhausted that then I would consider contacting LG and asking them. Although when I did that they didn't get back to for about a week.