"Mark as read" not working anymore on chats manually marked as unread

[pcworld]

I'm on Telegram Web A 10.9.44. For a few days now, the "mark as read" context menu does not have any effect anymore to clear a manual "mark as unread" flagged chat.

Steps to reproduce:

• Right-click on a read chat and select "Mark as unread". As expected, the unread marker appears.
• Right-click on this chat again and select "Mark as read". Nothing happens. Even after reloading the client or looking up the chat in another client, the unread marker stays. It can however be successfully cleared from telegram-desktop.

This worked fine some days ago.