Taskbar tiles disappear at random for applications located on secondary monitor

[AnrDaemon]

In multimonitor setup, when application is located on monitor other, than nTask itself, the application windows sporadically disappear from taskbar, and only reappear, when become active.
Very often observed with VirtualBox secondary screens, f.e., but even Opera may vanish from taskbar from time to time.

[AnrDaemon]

There, I finally did it!

[AnrDaemon]

This behavior, supposedly, subsequently cause a reorder of taskbar buttons.
Which is a minor, but annoying issue. When I work with nearly identical windows of the same application, I rely on their order staying unchanged through time. (I.e. GIMP dialogue windows.)

[NeonLightning]

i'm having this happen (firefox only one i've noticed it happening with right now) randomly aswell but when i tab to it it comes back.

[AnrDaemon]

Another category of windows, which get lost on the taskbar, is elevated applications.