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

[martin rudalics]

> 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