Tooltip Rendering Twice

[MSchmoecker]

There is a bug where tooltips are rendered twice, once correctly while hovering over the setting and a second one in the background. I've tested multiple games and it seems game specific, although it was only reproducible with Unity 6 so far.

• Valheim (Unity 6.0.46), the second tooltip is on the left:
• Tower Factory (Unity 6.0.51), the tooltip mirrored and on the right this time:
• The Farmer Was Replaced (Unity 6.0.43): The bug did not occur
• Empty Unity 6.0.46 project: The bug did not occur

For Valheim, I added a debug log Debug.Log($"OnGUI: {Time.frameCount}"); inside void OnGUI(), with the result that OnGUI was called multiple times per frame.

Adding GUI.tooltip = string.Empty to the end of DrawTooltip() suppresses the bug, although I think that's just a workaround. My guess is that a canvas or camera setting