bug#15957: 24.3.50; Follow mode scrolling broken on Emacs trunk

[martin rudalics <rudalics@gmx.at>]

 > I really doubt that the code in `follow-scroll-up' is broken.

I didn't say so.

 > Follow-mode
 > is designed so that the rearrangement of the other windows (the ones that
 > follow the selected window) occur in the post-command hook (to allow
 > Follow-mode to act upon all Emacs commands, not only it's special
 > function). It appears that something has changed in the display engine, or
 > in the way that post-command-hook is called, that makes this mechanism
 > fail. This could also account for the difference we see when the function
 > is called via a key sequence as compared to via M-x.

IIUC we'd have to find out when and where follow-mode expects the
selected window to be a certain window and why this sometimes fails.  So
maybe you should try the change I suggested.

 > This is also the reason why reported this as a bug, rather than digging
 > into the code myself. However, I could try to add log code to Follow mode,
 > to check if I could try to figure out what is going on.

Please do that.

Thanks, martin