I get the feeling that you're talking about Cakewalk bug-fixing z3ta+ (the original - not the upgrade). Z3TA+ has been around for a very long while. There are two or three versions out there still in use. There is the RGC Audio one and the purchased version by Cakewalk with some very minor changes and a different file structure from the original one. Most problems come from people not noticing that there is a difference between versions and trying their RGC Audio hacks on the Cakewalk version with varying degrees of success. The unaltered synth is very stable with one caveat: it was made back in 2002 I believe. There are very few vsti made in 2002 that people are still running today. They tend to be a little buggy on today's hardware and operating systems. I don't know any company that goes back that far and makes a free update for existing users. The usual path is if the company feels that the synth still has merit then they revisit and update it to today's standards. Z3TA+ held up extremely well with today's synths requiring mostly workflow and fx updates. Also the upgrade was discounted rather heavily for a while before the regular price was in use. I think Cakewalk was more than fair with the upgrade price, and they are always running specials. There isn't any reason that someone couldn't wait for a sale and get z3ta+ 2.1 at a very low cost.

Now, if you were talking about z3ta+ 2.1 and saying it was buggy then you're wrong. If you do some research you'll find the problems that others were experiencing were audio driver issues solvable by ASIO4ALL in most cases and some standalone issue conflicts with other running software (I'm not sure what the verdict on this was). There are plenty of documented issues with people running the various cracked versions out there (solvable by just buying the software). Maybe that's what you saw?