actually there is one more bug related to apps opened in foreground but already reported by me to Jolla.
Open app for example Messages
Lock the screen
Unlock the screen by double tap
Open menu by swiping from the bottom (on the lock screen)
Try to open Messages by taping Massages app icon. On the first tap nothing happening. On the second tap you can see opened app.

So it looks like they have some problems with opened apps and lock screen.