Last document at DTTG start

Whenever I start DTTG after a pause it starts with no selected document:

Is this the normal behaviour? I would prefer DTTG to start with the last document on the last page I’ve read. DTTG does this, if the last use was not long ago. But after a few minutes (I can’t say exactly how many) DTTG restarts with the above screen.

I suspect it’s because iOS closes apps that haven’t been used for a while. But couldn’t DTTG save the last document with the current page locally and load it when needed?