What I'm thinking is:
In AF-S focus mode, if you have the camera setup(as most folks do) to expose on AF confirmation then it could make a bit of a difference to the way MO works.
Firstly: on the camera you may have a choice of priorities when in AF-S mode: 1. release(or
shutter) priority or 2. focus priority.
That is, the camera will allow you to take the
exposure even if AF hasn't been set(yet) in 1. This allows you to keep on spraying .. long after you've stopped praying!
If OTOH, you use 2. mode, where the priority is on AF, if you don't achieve focus the camera will not expose, allow
exposure or even respond to heavier pushing on the release. It feels like the camera is locked(it's not, that's the way it works).
So if you get focus, and then tweak focus a bit, in release priority mode(2.) the camera will lock up again. It knows that focus is no longer set, so you need to start the AF acquisition process again.
I don't have this
lens so can't confirm, but ... this MO mode seems to indicate that if you set the
lens to MO mode, you may be able to still make
exposure even if you have no reset the AF confirmation point.
Someone with a camera that allows
exposure priority settings in AF-S mode.
I'm assuming that MF mode is simply manual only and no AF at all.
Would be interesting to see if this is the way it works.