Full disclosure...I'm on the latest Insider's Build and it isn't really a bother.
I have a Surface Pro 5 and have a similar experience but only when using the pen. In that case both the Start 11 and Windows menus open simultaneously all the time. Using finger touch or a mouse always works fine. This has happened for as long as I can recall and only when using the pen.
As I am on the Insider build, I have no expectation of a fix nor is it an issue for me. I just wanted to share this.
Thanks
Love the product!
I appreciate you are fine with this "feature", and Start11 is all-round a great improvement on the native menu, but I find this bug very annoying and the fact is it shouldn't be this way.
Mine do not open simultaneously, it is completely random which one comes up. Clicking the start button may bring up the native first, then I have to click on another part of the taskbar to get rid of it, then click the start button again which may or may not bring up the native or Start11 menu, and so on and so forth.. Not the way it should be.
I wonder, when your menus open simultaneously, how are you able to click on any of your icons on the menu that is underneath? I assume this is Start11, surely this must render that menu rather useless if it is always being covered by the native menu?