When two hidden blocks are below each other, context menu of activities/resources near the bottom of the upper block is not fully accessible. Only upper links, those not overlapping the second topic (hidden as well!) are clickable. The other links are not highlighted on mouseover, nor the mouse pointer is changed. They can be clicked but nothing happens.
1. Log into a course as a teacher, turn editing on.
2. Create TWO HIDDEN topics.
3. Create any resource/activity in the topic ABOVE - will be hidden as well.
4. Click context menu on the right.
A set of links which overlaps the topic BELOW will not be highlighted on mouseover nor successfully clickable.
This seems consistent in different browsers and different themes (Clean, More), and I also tried in one old Moodle 2.7.2. Screenshots below.