Dota 2 chat

Okay, I have searched everywhere trying to find if anyone else is having this issue, and I found nothing.
So, in Dota 2, when I am typing in chat, after a random number of letters typed (usually between 1-3), blinking text cursor ( ' | ' ) moves to the far left (beginning of chatbox).

Obviously this makes it almost impossible for me to write a sentence someone can read without problems. Outside Dota 2 everything works okay. I hope I put this thread in the right forum, and I hope someone can help me with this very annoying issue.
Problem occurs in all sorts of Dota 2 chats (ingame, gamelobby, channels, ..). Chat via Steam works normally.

If needed I can include a short video showing this problem.