BUG? Session not saving when returning to Song mode

I have a series of Patterns in Patterns view. Currently, one of my Patterns is 16 steps long, but I want it to play for 64 steps. In order to achieve that, I duplicated a Track page to make it 64 steps in length (but the Pattern’s remaining Tracks are still 16 Steps in length).

I tap the [Save/Reset] button and see the Session saved confirmation. I switch to Patterns view, tap the Pattern I’ve lengthened, hold Shift while I tap Play to play the Pattern chain. It plays back with my 64-step Pattern length as expected.

But once the chain is complete and playback loops around to the first Pattern in the Chain, I see a Session cleared alert and it loses my changes to my Pattern, making it 16 Steps long again.

I tried this multiple times and got the same result. Then, finally, it seemed to save my changes permanently. (And I don’t think I did anything differently.)

As a user, when I manually Save a Pattern, I expected that change to automatically be saved to my Patterns view as well… in other words, it seems like I have to save the same change twice in order for it to actually take effect. This seems like an error to me.

Am I missing something?

I tried to read up on how “Sessions” work in the manual, but there’s almost nothing about it.