Steps to reproduce:
- be logged into Wikidata
- ensure the preference “Add pages and files I edit to my watchlist” is enabled (under Preferences → Watchlist → Advanced Options)
- visit some item, e. g. the sandbox item
- make sure you’re not watching it yet
- add, edit or remove a statement
- scroll to the top of the page
Expected result: The star indicates that you’re now watching the page.
Actual result: The star appears to indicate that you’re not watching the page.
Workaround: Reload the page.