Additional: Through some searching I've found some on their M8's are having the same problem
(specifically the white triangle), but there has been no resolution.
On my T-Mobile HTC One M7 rooted stock phone whenever I send or receive a text, for a split second a small white triangle with and exclamation point appears in the top left site of my notification bar. I've tried keeping my notification tray extended to see if there is a message associated with it but there never is one. It's like a phantom texting triangle that I can't figure out . Does anyone else have this problem or know what I am talking about? I haven't been able to catch a screenshot of it yet because it blinks by so quickly, but I will post one if I can be speedy enough to get it.