When running Edge Dev, tooltips will randomly appear. The issue seems to be exacerbated when multiple windows are open. The tooltips will disappear when the window they came from is made active.
This issue happens fairly frequently, and seems to happen more on Edge windows that are on other desktops. It doesn't seem to matter if the window is topmost on that desktop or not.
I have only noticed this issue, however, when using the precision touchpad on my Dell Inspiron 7573 2-in-1. Using the system with an external mouse seems to mitigate the issue.
While the tab bar at the top is the most common cause of tooltips appearing, it also occasionally happens to links on webpages, sometimes on inactive tabs. When the issue occurs on the tab bar, the tab is highlighted as if it was being hovered over.
It's a known issue with Edge insider which @josh_bodner also confirmed in one of his posts, it's caused by virtual (multiple) desktops. I've seen other people reporting the same defects related to multiple desktops