Version: 53.0.2785.89
OS: Windows 10

This is not happening everywhere, but it happens at https://forums.frontier.co.uk/newthread.php?do=newthread&f=105.

0. Have spellcheck enabled for a language.
1. Type gibberish in a <textarea>, e.g. "asdfjkl aoeuhtns arstneio".
2. Right-click a red-squiggled word, e.g. "aoeuhtns". This selects the word and opens the context menu.
3. Choose "Add to dictionary".

Expected: Context menu closes and word loses red squiggle.
Actual: Context menu closes. Word remains red-squiggled. Right-clicking again shows the "Add to dictionary" option again; choosing it again continues to not remove the red squiggle. Moving the cursor to other words and trying again with the original word does not change the outcome.