Yesterday, I checked the optional Windows updates and noticed a new Samsung MTP driver. So I updated the driver and when I connected the tablet running on 4.1.1, the device was not detected. Today, after I got the OTA update, I tried again to connect the tablet and it failed to detect the device properly.
These are the steps I completed, that fixed the MTP issue:
1) Open the Devices and Printers in Control Panel, the tablet should be listed under Unspecified devices.
2) Right click on it and select Properties.
3) Click on Change Settings button.
4) Go to Driver tab and click on Uninstall button.
Make sure you check the Delete Driver option, when you uninstall the driver.
I did not have to reboot the computer, by simply connecting the tablet Windows detected the new hardware and reinstalled the proper drivers.
Now I can access both my Nexus phone and tablet, using the same cable and through adb.
Not sure if the combination of both 4.1.2 and new Samsung drivers helped, but the above steps fixed the MTP detection issues I had. Check the Microsoft driver date, is from 2006???