I have tried to reproduce the issue on my end and its working fine as i was able to add and remove the bate numbers from the PDF file.
Is this an issue with a particular PDF file or with all the PDFs? Please try with a different PDF file and check. Also, please share the PDF file in question with us so that we can check it at our end.
Please try to repair the installation from the help menu (Win only) and reboot the computer once.