When using FX in the main editor on an instrument that uses phrases, the DSP block size in Jack effects the resolution of the effect. This occurs in both playback and rendering. It doesn't occur when using ALSA. It also doesn't occur when not using a phrase.
Steps to reproduce look like this:
Start renoise on Linux using Jack
Create an instrument with a simple phrase:
Add some data with glide effects in the main editor (not the phrase editor):
Change Jack's block size to something like 2048.
Smooth gliding between pitches,
Stepped transitions between pitches.
Block Size = 64