Splitting cells breaks collapsible headings

[mxxun]

Given two header cells, first collapsed (with section under it hidden), and second immediately following the hidden section, splitting the second with Ctrl+Shift+Minus hides it and its whole section.
Reloading the notebook or editing and executing any Markdown cell unhides them as is proper, but having a whole section disappear without a trace is unsettling.

[jcb91]

having a whole section disappear without a trace is unsettling

Absolutely, this isn't really acceptable behaviour. The reason it happens is that headings don't get reconsidered on calling cell.set_text, but on a bunch of other occurrences. I think this has caused similar problems before, so it probably makes sense to patch the MarkdownCell.set_text method directly...