What's supposed to go inside that "learn more" dialog is the page's lede section if there's no comments within it. (That's why Redrose64's talk page doesn't have it hidden -- it has that "welcome" message that's signed.)

The entire page being wrapped in a div is presumably confusing the parser either by:

1. having it think the entire page is the lede section and there's no comments in it
2. having the part that's pulling out the lede section get confused and expand out to extract the covering tag

I think the only correct think we can do here is skip putting things into the "learn more" popup when there's markup like this. (Working out what tags are crossing sections and extracting just the bit inside the container before the first heading feels like a recipe for rendering issues. Closing-and-reopening the tags also feels like a recipe for rendering issues.)

Maybe this is a case where this processing can get moved to DiscussionTools, which I think already has a better handle on what's in the top section than mobile does. Once the system knows it's in the top section, then it can do balancing (or as it happens, DT already does, to handle this exact case, see comment at T271588#6733745). Or perhaps, some (more) duplication can be plopped into MF to fix this (c.f. lead paragraph processing).