Porbably this was alread reported, but I couldn't find it, so I am really sorry if this is a duplicate 
How to reproduce:
- Enter this in your chat:
XXXXXXXXXXXXXXXXXXXXX <============
- Then this:
OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO
- Then open your chat and press the UP-ARROW key twice
You will see that the half of the text is missing even it would fit perfect in the line
Comment by kingsupernova: this happens because the game saves the distance that was scolled over when moving to a different message.