Similar issues were reported a few years ago, and in recent years as well, but usually associated with Kontakt 5.
However, this is not a Kontakt 5 issue. It seems to be the host DAW overloading VEP5 with tempo change messages.
In Nuendo 7, even a single note sent to a local instance of VEP5, with EW Play loaded, will cause VEP5's loading to peg at 99% for the duration of the tempo ramp. This is what causes distorted playback of those samples. With Digital Performer 9, I can see VEP5's processing load jump up intermittently during tempo changes, but only to around 60-70% (from a normal 20-30% in my test case), so it never "overloads" VEP5. Perhaps even with curved/parabolic tempo changes, DP is using a lower resolution set of data points to "paint" a tempo curve (hence it acts more like a succession of jump points in Nuendo, where Nuendo apparently uses many more data points for it's ramp function).
The workaround currently is to set Cubase/Nuendo's Tempo track and editor to "Jump" mode, and draw tempo any ritards/accel with the pencil tool in the Tempo Editor. I can only assume Cubase/Nuendo is sending too many tempo change messages to VEPro when using it's "Ramp" mode, overloading it's tempo processing.
To me, the simplest solution would be to provide a way to turn off receiving of tempo change data within VEPro completely. I don't even need it with my current template. I see no reason for tempo change messages to go to VEPro if you aren't using tempo sync'd libraries (such as orchestral libraries - VSL, etc). And given this bug, tempo sync'd libraries often won't work with tempo changes without this distortion problem, or at least artifacts.
Even some tempo sync'd effects and VIs loaded internally in Cubase/Nuendo won't respond reliably to tempo changes, so tempo sync, for now, really only works with fixed tempo material - hence, there is no need to globally, perpetually send or receive tempo change data with externally hosted VIs. Is there a way to filter or turn off tempo change receiving in VEP5, or can such a parameter be added?
I have reported this to Steinberg several times, but so far no word on a fix, and it may have to occur on the receiving end anyway (as some users may want tempo change data to be sent to some external devices, but not VEPro, or vice versa).