Synchronisation of Cubase VST

I have 2 old Cubase versions: SX and VST. My problem is about synchronisation. The master in my system is a DAW (digital audio workstation) which sends MTC. When SX is synchronized as a slave everything works fine: it starts as soon as it gets the MTC time code in and it stops, when the master DAW stops. However, the Cubase VST version starts as soon as it gets the MTC, but IT DOES NOT STOP when the master DAW stops. It just keeps running on. Can anyone tell me, what could be wrong?

Did you check to see if VST was still set for external sync when you stopped the master? Thinking there may have been a rogue command shifting it back to internal after you started it.