Please check out this thread and try the suggestions posted there:
Bug Resolve Suggestions and Bug Report Template
If none of the suggestions work, please create a bug report conform the correct template in the link I just provided.
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EDIT:
I think I understand what you're saying now.
This is a old bug, and I can confirm it. It was also present during the Winter Event quests.
Description: If you have (new) quests, sometimes they randomly pop up when you're at the Market, doing trades.
This happens whenever you accept a trade.
It seems to be a cache issue perhaps. A reload usually fixes it, or just accept or use the X to close the quest.
Not sure what triggers it though.
- L