• Set your panel to "Windows can cover" mode
• If you don't use them, create at least 2 workspaces
• I used a KWin window tiling management script (but I think this step is optional)
• In a workspace #1 open your default Internet browser
• In a workspace #2 open any GTK application (aka. Telegram) that could display any clickable URL and make sure that its window almost touches the edge of the screen closest to where your panel is placed
• Inside of your GTK application open any URL by clicking on it
• Check the weird behavior of your panel that you configured in step 1 at the top (your Telegram window will not cover the panel unless you visit workspace #1 and make a focus on your browser window first)

There are a few similar glitches whilst working with multiple Virtual Desktops, GTK applications and optionally any window tiling manager. "Auto-hide" and "Windows can cover" options usually start being inconsistent (from user's perspective).

Bug reports do not belong to the forum, please report this to https://bugs.kde.org