I had the same thing happen with my Delta Jointer. the power would not
shut off. It was intermittent and the tech thought there was nothing
wrong with it. I should have called Delta, but went to a local repair
shop in Raleigh and got a replacement for abt $22

Chuck Taylor wrote:

One of my recent "new" machines (acquired at the same time as the
Unisaw that was the subject of another thread several days ago, and
which made the trip home just fine, thankyouverymuch) is an
Invicta/Delta 22-650 (aka Rockwell RC-33) planer. 220V, 2HP, single
phase motor.

While making space for these machines and setting them up, I turned on
the planer for a few seconds, then flipped the switch to OFF. The
planer kept running. It took a few more flips of the switch before
the planer stopped. I repeated the process and had the same
experience. It didn't do this when I tried it out at its old
location, of course.

With the power disconnected I checked the switch terminals for
continuity. So far I haven't been able to duplicate the problem--that
is, to get continuity with the switch in the OFF position. (It's a
double-pole switch, and both pairs of terminals behave like they ought
to when probed with a meter.) Nothing looks or smells out of sorts
with the switch.

Unless someone suggests another possiblity, I'm going to assume that
the switch is faulty in some way that doesn't show up at low
voltage/current, and that it simply needs replacing. Anything else I
ought to check first?