Thank you for the video example, that makes it much easier to understand. I'll look into it straight away.
Edit: Unfortunately I am not able to replicate the issue on my PC, but I did revert a few changes to the waveform sampler that I suspect may be the cause. I've just updated both instances of 0.4.12 with this reversion in case it is the cause.
If this change doesn't fix it, let me know if Windows 0.4.11 has the same issue, and if not I'll compare the changes.