Dell Latitude E7240 issues

Hello,

So my company purchased a Dell Latitude E7240 laptop with the E-Port docking station (the one with just 1 DVI/VGA connection).  The laptop is fine by itself but it has issues when we undock it and then re-dock it.  The problem is that the user (just happens to be the President of the company :() has 7 or so USB devices and since the docking station only has 5 ports available, we bought a separate USB hub for her (and the USB hub has its own AC adapter).

So if she has the laptop in the docking station docked and turns on the laptop, everything is fine.  However, whenever she undocks it and then docks it again none of the USB devices work.  The problem is that it doesn't happen every time she undocks and re-docks but enough that it is extremely annoying.  Also when this happens, the laptop won't restart or shut down without any issues...it just hangs at "shutting down Windows" screen.  I have to manually hold down the power button to get it to shut off.

We have had a Dell tech come out and swap out the motherboard on the laptop and that seemed to fix the issue but a day or two later the issue cropped up again.  I just received a new docking station from Dell and swapped it out but, again, still having the issue.

The laptop is Win. 7 64bit OS load; has all the latest drivers that I know of...so....anyone else with the similar experience and/or any thoughts on how to fix this?

Thanks!