I just tried task 4 in 0.6.40 Linux and I see the weirdness.
Using the TOC to jump to Task 4, the scroll bar is at the top in ebook viewer.
Click the Scroll bar Up arrow and nothing appears to happen.
Click a bunch of times (about 6 times) and the view jumps to the start of task 3
The scroll bar is now somewhere midways.
You can scroll down using the scroll bar arrow heads until you enter Task 4.
Click the arrow heads some more and All of a sudden it jumps to "Where to get help"
This is appears to be a Viewer bug when transitioning split HTML segments.