"And the nice thing is: If you do nothing, you will get an overspeed."
This appears to be contrary to all my manuals, "Static" (both for the 767 and 747-400). According to these, the aircraft should leave the path if the aircraft is unable to maintain the path by increasing its speed (i.e. by up to 15 kts(in the VNAV idle phase)... but only if this extra 15kts does not violate any VNAV speed restrictions or Vmo/Mmo).
"You will find the information you require for the 757/767/ 747-400 des....in the book called "FMC Users Guide" "
Thanks, "Scanscanscan", but I already have this manual. No mention of bug behavior seems to be made in the chapter concerning VNAV descent. I may have to put question to the Bluecoat forum.
Rgds.
Q.