There appears to be a problem with creating new castbar.

I created a new castbar to be used as an enemy cast bar. After creating it and setting the unit to target, I exited and both cast bars were now set to target including the one that used to be my chars cast bar. After experimenting it appears that if you set a cast bar the way you want it and then click on an existing cast bar it will change that one also. I was clicking on the other bar just to verify that it's unit was correct.

It appears to work if you go into button edit mode, click on a cast bar, set it up the way you like and then exit button edit mode. Clicking on an existing cast bar before you exit button mode appears to change it.

Interesting, this should be fixed in the new GUI. I'll make sure to address this in that new codebase