How does that document address the question? I can't find how it does.

Question: is this an all-the-time-it-always-works-this-way problem, or is it
intermittent?

Should one expect that if a new folder is created and security groups  are
assigned to it, that they have to wait for a restart  of services for it to
take effect, or can one expect to try, and if it doesn't work, then they'll
have to wait until the next restart?

The best practice is to assign groups  to the roles in SPS and then
assign users to the groups in AD. This will sove the problem  well.

The best practice should be best practice only and should NOT become
NECESSARY as in this case !

It's not necessary.. You should feel free to add  people individually and
wait until the next reboot for it to take effect... Entirely your option.

It is not all the time... In fact, some sites don't have the problem  at
all. But for me it is enough of the time to plan for it.