If you enter Steam Big Picture, the panel disappears fine, but if you open and close a game, there's a delay between when the game closes and when Big Picture reappears. When that happens, the panel won't disappear unless Big Picture is closed and opened again, so it just sits on top of Big Picture.
I cannot reproduce this issue with current Plasma from master and current Steam. Is this still reproducible for you?
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This bug has been in NEEDSINFO status with no change for at least 30 days. The bug is now closed as RESOLVED > WORKSFORME due to lack of needed information. For more information about our bug triaging procedures please read the wiki located here: https://community.kde.org/Guidelines_and_HOWTOs/Bug_triaging Thank you for helping us make KDE software even better for everyone!