Well, I'm actually not completely sure how long it was happening, but I was digging dirt piles, and thought, wow, I'm not getting much dirt because the empty 2d slot for Urth wasn't filling up (didn't have the bag open, just watching the slot numbers). Opened the bag and realized I had like 40 lumps of Urth, and that's when I realized they changed the stacking.
I also noticed recently that my Pi pies stacked...that's probably been around for a while too, but I only noticed it over this past weekend. Definitely appreciate that they are fiddling with the stack sizes...makes it so much easier to carry a lot more around.