Sometimes, instead of expanding the text area where you're typing a message by adding a new line and breaking text, the entry expands as much as needed. This of course means most of the time that the chat window gets immediately out of the screen on the left side, which is very annoying to fix because the borders are not visible.

This behavior is very weird, but it doesn't happen all the time; yet I couldn't understand when it is triggered. At least, it's fully reproducible once it has appeared: currently I'm not able to get the correct behavior.