Shipped in 8.4. On the free tier, you only get one unlocked vial at a time. Until now, that unlocked one was whichever one ended up first in your sort order — which could shift unexpectedly.
Now you explicitly pick. The active vial always pins to the top of Calendar and My Stuff, and tapping a locked vial card pops a clean Make this my active vial chooser. No paywall trip just to swap which one you're tracking this week.