bug#16678: 24.3.50; REGRESSION: text selection is broken in Customize edit fields

[Drew Adams <drew.adams@oracle.com>]

> If I highlight inside the edit field, everything works as expected.
> That is instead of
> 
>   Put the cursor before the `[' and hit `C-SPC'
> 
> I do Put the cursor ON the `[' and hit `C-SPC'

That is what I meant.  I should have said "put _point_ before..."
or "put the cursor on...".

> then I get the expected behavior.

This is very weird.  When I try now, I do not see the bug.
Last night it was entirely reproducible, from emacs -Q.

The behavior I saw was that selecting the entire text in the
edit field unhighlighted the selection.  IOW, selecting the
last char in the field caused unhighlighting.

No matter how I tried to select all of the text in the field,
selecting the last char made the highlighting disappear.
That was the bug I tried to report.  For example, just
double-clicking the `[', which selects the whole text `[next]',
did not highlight the selection (perhaps it highlighted then
unhighlighted it).

The text was in fact selected, as I tested by yanking it.
But the selection was not highlighted if it included the last
char.

> What is the purpose of highlighting outside of the edit field?

To be clear, I never tried to select beyond the last char.
I was only selecting all of the text in the field, _including_
the last char.  For example, C-SPC followed by <right>...
until the cursor moved past the last char, to select it.

But as I say, for some reason I cannot repro the bug this
morning.  I will keep an eye out, to see if it happens again.
But what is weird is that it was reproducible over and over
last night, but not now.

And I in fact still have an Emacs session (but with my setup,
not from emacs -Q) that shows the bugged behavior now.
I tried poking around, to see if I could discover something
different about that Customize buffer, but I haven't found
anything.

If you have an idea of something to look for, and you let me
know soon (e.g., before I forget and quit the session at some
point or the session crashes), let me know and I'll take a look.