> AFAICT the problem is that sometimes this heading is already hidden
> (because of a preceding subtree covering the current one), so we end up
> going back to the preceding/larger subtree and re-hiding it.  So for
> a subtree like that of `;;; Code:` covering N smaller subtrees that were
> previously hidden, we end hiding the `;;; Code:` subtree N times (and
> each time, this requires looping through all the covered headings),
> which introduces an O(N^2) complexity.

The patch below seems to fix it (and bug#78673 as well).
Juri, comments?


        Stefan