Quick switching of the source will label the wrong source

[cafarm]

To reproduce:

1. Add a source with a nested source
2. Select the nested source
3. Press up on the keyboard to change the selection to the parent source and quickly press the add source button
4. The GUI will think the nest source is still selected when adding a new source
5. Add the new source to the nested source and try to modify its label
6. The parent sources label will be change instead of the nested sources

[cafarm]

This turns out to be a pretty tricky problem and one that may be more work to fix than it's worth. This happens because, if you're quick enough, you can interrupt the selection of a new source with an action like pressing "Add Source". After you've added a source, MATLAB will then finish running the interrupted select node code and think the wrong node is selected. I'm not aware of a good way to make node selection non-interruptible.