First of all thank you so much AllanR for the detailed explanation and the recreation of the file, I appreciate you're taking the time to help!
So before I saw your file, I messed around with the code again... trying to make it as simple as possible.
And I almost got it work but... I got lost when it comes to DeSelect! as you can see (file attached) the code is VERY SIMPLISTIC and I feel that there must be a simple solution to FIX what I'm doing wrong here.
Basically, I created another object that supposed to be followed by the SELECTED OBJECTS (family) only.
After I had a look on your code, I realized how complex it must be (very confusing for somebody like myself to be honest, BUT! it works). As you already understand I'm not just trying to Copy/Past code that's why I'm still trying other solutions to different problems I'm having and probably will run in to more of them...
I'm guessing that what happens is something like you described, there must be a CLASH between the selected and unselected objects which cause the mess.
I still feel that with this creative yet simplistic way, maybe it can be fixed and I just don't see it like many other issues miss, even when I think "logical" first on paper, I can't see the solutions to the most simple things when I get back to C3 code... there is no doubt, I much more to learn.
Of course I tried to play with 'Is Selected' because it made sense to me that ONLY the SELECTED objects should follow the 'Core_Selector' Object, but after I tried different ways to 'CLICK' to not just deselect after drop the mouse button, but also get rid of the 'Core_Selector' as it's job is temporary.
My different tests are not on the code to keep it clean as possible for you to see, but I did try to play with INVISIBLE (enable disable) also dedicated layer and even change it's position and such.
The goal is to make the 'Core_Selector' invisible at the end (once it will work) for now it's visible so we can see it while playing with the code.
Maybe if you'll have a look on the file you can see a simple solution in the spirit of what I started?
Because once again, IT WORKS! but not complete, and I would love to learn if there is a simple way to go with this creative solution I tried so far.
As I'm very hyped now that it works (almost) with the current 'CODE' I'm still playing with it but still, I have a strong feeling that you'll find a simple solution within 5 seconds and LOL as hard as it gets...
I hope that the upload file works this time:
Thanks ahead for any help!