Why is Cakewalk changing Clock source?

[norfolkmastering]

My Cakewalk set up includes an analogue tape machine which is slave locked to Cakewalk.

Cakewalk is set to Clock\Source\Audio.

Occasionally during operation, Cakewalk will change its clock source to SMPTE/MTC for no obvious reason.

Any idea why this is happening?

[57Gregy]

Is there any audio in the project when this happens?
 

[norfolkmastering]

3 hours ago, 57Gregy said:

Is there any audio in the project when this happens?
 

Yes there is audio on multiple tracks.

[John Vere]

You didn’t really say what the tape deck uses for syncing? 
Last time I did this 20 years ago the multi track used MMC and that’s what I set Cakewalk to. There was a few things I forget but I basically followed the instructions that came with the multi track. 

[norfolkmastering]

I'm syncing a Fostex G24S to Cakewalk.

Cakewalk outputs MTC which (using a PC app) is converted to LTC which is input to the G24S external sync input (The G24S supplies the 'slave' LTC from track 24).

It all works really well and sync is tight but every so often Cakewalk changes its sync source from Audio to SMPTE/MTC, almost as if its decided to slave to the G24S (which is not what I want!)