stuck notes with vst~

I found different threads over the years with the question about stuck notes with the vst~-object with certain plugins such as Fm8 or Absynth from NI, but no solution.
On most software-instruments the vst~-object is working fine, but on some not.
Today I was using Omnisphere from Spectrasonics and the same problem appeared.
The problem is not about lost Midi-Off-Notes and using flush doesn´t help, and even a simple vst-player like the one in the "inVeSTigations" shows, that some vst´s are working perfect and some have this problem.
Did anyone found a solution so far, and maybe an explanation why this happens, because I would like to use Omnisphere in a installation.......

best wishes
Kurt