A charging scanner causes the said message every ~6 sec after it is charged while you stay in build mode and use the left mouse button.
As far as I could see the use of the right mouse button stops this (that is what the message tells you to do)
1. there shouldn't be any message from the scanner system while in build mode
2. there is no "Scanner charged" Icon as an effect symbol on the screen when the scanner is charged.
overall not a big thing... just annoying