There is a problem with the Device Is Connected on the Device Maintenance And Connection screen.
I was able to reproduce the same result more than once.
1- I selected a Device on the Device Maintenance.. screen
2- I closed this window
3- The Selected Device showed up on the first line of the McStudio main window.
4- I builded the application and loaded the program to the device with succes
5- The Selected Device is removed from the main window of McStudiothe new Selected Device being 0000FF00.
6- I open the Device Maintenance ... screen and my device is still showing as IsConnected