Unwanted text scrolling when help window appears

[diamond-lizard]

Steps to reproduce:

1 - Fill a buffer with more than one-window's worth of text.
2 - Split the windows horizontally (one window above the other).
3 - Open a help window.

At this point I expect and desire the text and point in both windows to stay where they are (as they do in default emacs behavior, as can be seen under emacs -Q).

Instead, the text in at least one window is scrolled (apparently to to location of point in the window which had focus when the help window was opened).

This undesired behavior is present whether or not Popwin:Adjust Other Windows is toggled on or off in M-x customize-group popwin