Bug or intended : (i guess bug)
The red global Transmitter has a small issue
Place a red channel transmitter, change color, place a red channel receiver give it a signal and repeat this step, then you can have 2 or more of the same red channel transmitters, with there own receivers....
Catch of this, if you delete one transmitter, the other receiver may pick up the signal of the first placed transmitter
If this is intended : then the bug is that all other ones can't do this....