Two adjacent Edge instances end up on top of one another after Relaunch

OK, I have been able to get the bug to repeat on my Surface Pro 4. It has Edge Canary 76.0.146.0, no extensions installed, no flags changed. The Surface is running Windows 10 Build 18890.

1- Launch two instances of Edge Canary

2- Place them side by side using Win + arrows

3- Open Edge://flags

4- Look for Microsoft Edge theme

5- Set it to Enabled

6- Relaunch

7- The two windows will reopen not quite where they were first placed, are slightly smaller and overlap a bit. Otherwise, the behaviour is ok.

8- Go to the Edge://flags window and set Microsoft Edge theme to Default

9- Relaunch

10- The two windows will be almost perfectly on top of one another. One will be slightly recessed, both vertically and horizontally.

As I said, these steps are repeatable on my Surface Pro 4. I have been able to repeat the same steps five times and it always overlaps the second time I relaunch Edge. However, the bug has proven evasive on my workstation. So far, it hits when it wants.