Sorry for the delay in responding, but it took me a bit to reproduce what you were seeing. I can confirm seeing the same behavior above, on Global server (I expect its the same for all).
I need to do a bit more digging to confirm whether this is in fact a ‘bug’, or it is actually working as designed. Basically, just because you have been given Manage access (or more specifically, View submissions access) on one project - ie the parent submissions - the child form could well have also been shared with other users who have not been given access to the same parent form. Hence, why should they now be able to gain access to view the parent submissions - by virtue of them being shared via dynamic attachments to the child form - just because you might have access to the parent. That may explain why attempting to cross-connect between two different shared parent/child forms may not work: to avoid potentially sharing (parent) submission data with other users who dont actually have permission to see that shared data.
I’ll do some more digging to confirm (or refute) this and report back.
