Hi
That sounds a bit odd.
OK..As I understand it...The first export (avi or mp4) was correct and the S/T were present.......So it's not the version you are using.
So, one question is....Why, as it seems, did you reload the Video you made? If you wanted to add further clips or edit your S/T etc, you should have saved your project as a vpj file and then reloaded that.
Here using VP 7.21 The Exports are complete and the vpj file reloads everything back correctly and added clips and more S/T export as expected. I can't find an error here.
Nevertheless, reloading an exported clip that already has your S/T should not have made any difference as they would then have been part of the video. Any further S/T added to this video should have behaved in exactly the same way as adding S/T to any other clip. (i.e. like your first working export.)
Were the S/T visible in VP when you reloaded your first exported video? (They should have been as they presumably played in your external player)
As I said adding further clips and S/T to this should have made no difference.
I am afraid that hasn't helped but offhand I can't see where your error (if indeed you made an error) lies. It could be someone else may come in on this.
Nat