Hi,
some people who use the parallel port and Mach3 have reported similar problems with the latest (three updates to my knowledge) MS updates.
It may be that Mach4's parallel is similarly affected.
The Darwin parallel port works OK, or at least has done, but there are features like lathe threading and THC that it doesn't have, nor will it ever have them.
Mach4 when it was first devised was always supposed to be operated with an external motion controller. To get the best of Mach4 I think you will have
to buy a suitable controller.
Craig