This is probably an artifact of resampling to powers of two.
Yeah I guessed as much, but I assumed it was a bug and not a feature, since it was not present in the previous version(s?) of r1gl.
Resizing the icons to 32x32 (from 24x24 that they were) does remove the problem.
Hopefully it will be fixed in the upcoming versions of r1gl, but if it not, I can totally live with the blurring. It's not like I can't read the icons.