[NTG-context] Linespacing modified across document

Dear list, I've noticed that in my document the linespacing (verified with \the\baselineskip) is not consistent across the whole document. In the first section, it's fine (no maths). Later on, it gets increased by some amount, which tends to depend on what kind of mathematics are in between, so it's not constant. Has anyone else noticed this too? BR Alex