Threading has always worked well for me with the ESS although I do recall I had some issue with it about a year ago when I tried an updated plugin. It was definitely not the problem you are describing though.
If you attach your xml I will take a look and see if I can find an issue in it.
I would also suggest you may want to try an older plugin, sorry can't recall the one I am using but I think it was one of the first ones.
One other thing, if you are using ver 066 of Mach then get rid of it and go back to an older version, 062 is what I use. That will be unlikely to have any bearing on the threading as it is done internally in the ESS but there are lots of other bugs in ver 066, especially with Lathes.
Hood