Strange edges in unwrapped EPI phase maps

[tsalo]

After rescaling according to the FSL instructions and unwrapping with PRELUDE, I still see odd edges in the phase data, as below:

The edges are not stable across echoes, so the calculated phase-difference images end up with odd edges as well, as below:

This happens with both MB EPI and single-band reference images, but not with the field maps, so I wonder if it's something to do with the sequence or with the long echo times.