I wouldn't call this a bug, but it is a bit of an advantage. Basically, I realized that you can hide an entire sub beneath another sub if you launch them both within 10 minutes of each other. The one on top hides the one beneath, and zooming in isn't enough to reveal this. Am I missing something?

I'm pretty sure the tail would stick out a bit for the second launched sub.
You could also jump to arrival of one of the subs and use the time machine to get one of the subs to not yet hit the target to see its contents

This is a trick you can sometimes get to work once against a brand new player who doesn't take full advantage of the Time Machine feature.