Editing Physical Channel Does not Disconnect Previous Mapping

[jacobson3]

Steps to reproduce:

1. Create 2 double tags and add a DAQmx module to the engine
2. Add a new Analog Input line to the DAQ module and connect it to one of the tags.
3. Edit that DAQ channel and in the configure channel dialog, only change the physical channel.
4. Click OK and notice how the previous tag no longer shows up in the "Tag" column and it can not be written to from any other module.