Font weight, size and other current editing style properties are not preserved when Shift + Enter key combination is used and the user continues typing. Note: this is true not only for font weight but for other styling properties such as size, italic etc.
Thank you for sharing the exact steps, Rania. Continue following this item so you can be notified of any status changes on it.
Detailed reproduction steps: 1. Press ctrl+b to turn ON the bold font weight. 2. Type in the bold font weight. 3. Press ctrl+b to turn OFF the bold font weight 4. Type to make sure bold font weight is off. 5. Go to next line using the keyboard by pressing shift+enter 6. Text gets set to bold font weight on its own. This was observed on version 2016.3 1024, but I also tried it on the latest 2018.1 220 and was able to reproduce the issue there as well.