[Stone Knife]

I haven't tested this one, but I suspect that PT considers automation data as 'song' and keeps going until there are no more automation changes.

For example,
If you create some automation, then leave it 'behind'... PT may keep bouncing until it's passed the pan or volume or whatever changes that may still be there.

You may want to check for 'invisible data'.

Seconding the post above-, I've found that just making the entire project one big region as Roy suggested works in spite of anything left 'down the line'.
Tip:
(Make a Selection Memory Location and you can just click to recreate the bounce region without doing it over and over)