Here are some of the issues I noticed in X3d in my case. These problems aside, I haven't had any critical trouble and can still work with it just fine. Does someone else want to check or verify this list?
* horizontal track envelope line to the right visually changes up somewhat, if adding envelope point (just the point should be added)
* play cursor/line jerks, if playback is active and if mouse cursor is moved in the track view
* while plugin is on-screen, plugin jerks visually, if mouse cursor is moved in track view (visual information such as levels, frequency, not the plugin window, happened with Voxengo SPAN)
(* popup information in track envelope possibly not correct, if changing whole envelope line with multiple points) (for example, I selected all envelope points and wanted to move the whole line, and while one popup notification of a point showed for instance -6 dB and I grabbed the point to move up the whole thing vertically with Shift, the number shown was not in order. I was tired when I saw it, so I am not entirely sure. In fact, I have a headache right now :P)
Oh, I remember this was also the case with just moving one envelope point too.
Well, that's it. I'm off: I have other things to do.
QUICK EDIT: grammar error.