I can also confirm this behaviour, and have mindlessly (though annoyingly) handling it for some time. And now im here .

I am able (was able) to actively trigger the behaviour by having grouping 'on' in 'task manager' in my main panel. Having 2+ dolphin windows open, but minimized, as soon as I select group to restore window, the device notifier ('dN') pops up. If I leave the dophin window open, and go to task manager grouping and reselect same window from group, the dN pops up, basically stealing the focus. If click anywhere the dN disappears, but click again the same window in the group, the dN pops up, with no change to window. To note, what should happen, is the window should minimize--restore on each select in task manager, but this dN popup is interfering. It does not seem to do it with other groupings (so I'm thinking maybe something to do with 'Places' and its device list, triggering a refresh, which the dN responds to {?is this a dbus message}).

So it may be a temporary fix, but sofar no issue (yet?). I removed the task manager widget from my main panel, then created a new panel and added it there. None of this odd behaviour with dN. So I removed the widget and the new panel, and readded to my main panel. And now no annoying popup. Maybe this will work for others, if permanent is to be seen.

Like others, I have been doing upgrades for a long time, so cruft in the configs is exploiting bug'gers.
[[ KDE 4.11.5 openSUSE 13.1 ]]

KDE 4.14.8, Kubuntu 15.10.

My bug relates to the title 100%, however not so much as how it's triggered as most other posts that I read.
I get the Device Notifier pop-up whenever I change desktops in Kwin. I'm not sure if this is the expected behavior, however it's still bothersome.
I wonder how I can change this behavior.

I also confirm the problem (Debian "Jessie" 8.3, KDE 4.14.2). The Device Notifier window pops up if I try to switch between grouped windows (e.g. to the main window of of Lazarus or between konsole windows), sometimes over the system tray, in other cases even near left top corner of the screen.

The solution described above (viewtopic.php?f=67&t=117981&start=30#p334406) works by me only before first KDE restart
I found another temporary solution: I replaced the default task manager to an alternative ("Icon-Only ") but it is too inconvenient for me.

Update: now I recompiled task manager from KDE 4.10.5 and installed it, now all is fine. An useful conclusion: this bug occured after 4.10.5.