After configuring LXDE panel and setting Automatic hiding to on, the panel disappears when I work with applications (this is the expected behavior).
When I click on the start menu, and browse the apps, the panel disappears when the mouse pointer goes up in the screen and appears only if the mouse pointer goes all the way down in the screen.
I think the panel should keep appearing after click on the start menu until the user choose an application, or click outside the menu to exit.
In LXQT this works fine.