Garage wiring puzzle
Here's the answer.

It turns out there must be another junction box.  I made an incorrect assumption that Light/Junction #1 is the main junction.  It isn't.

It appears to be wired like this: Breaker feeds some junction that I can't see which then feeds Outlet A and Light/Junction #1.

So anytime the breaker is on, Outlet A is powered no matter what.

Really sucks if this main junction is in the finished garage ceiling and no way to find it without busting up that ceiling (cement/plaster type with lath of heavy wire mesh).  Jeez, all they had to do was put the main junction in the unfinished ceiling of the adjacent laundry room where the power cable comes through anyway.

Update: There may not be another junction box afterall.  See photos.  That's a very tiny access hole that I pushed my phone up against.  You can't see the full width of the joist bay.  Two cables coming back towards the camera.  One is the cable from the breaker and the other actually goes down the wall to Outlet A.  The two cables going horizontally to the left is odd, since the only thing over there is Outlet B.  More investigation is needed, but it looks like I might be able to feed a new 20 amp (12 gauge) cable through here, which is what I've been wanting to do.  Unfortunately, there's no access on the other side for Outlet C and this junction box can't be removed without busting up the ceiling as the cross bar mounting goes through the box.

Update 2: There is indeed another junction box, but it is not hidden.  Well, sort of.  The furnace duct in the garage is very close to the wall where Outlet A is.  The photos I took put the junction much closer to the wall than the known Light/Junction #1.  Sure enough, there is another Light/Junction "hidden" behind the duct.  No bulb in it, so I never knew it was there.  But this is definitely the main box for the garage.  Whew!