To reproduce, run attached application. It shows 2 lines on top of each other even though there should be a spacing of 1.5. According to this, plain number means multiplier for font height, but Qt treats them always as percentage: http://www.w3schools.com/cssref/pr_dim_line-height.asp

Browsers handle this properly and as a result, copy-pasting text from google docs into QTextEdit causes this problem to be seen. Example document that can be used:

https://docs.google.com/document/d/1fcRCOrvkxpVC3I6xXp1hYBpHhf9pL3mNqPXjUd4Kvfw/edit