[NTG-context] Setting expansion depth limit for metapost

I'm preparing quite long presentation -- nearly 3000 sides, 900 figures (500 distinct PNG files). I'm using ConTeXt MkIV installed using minimals (2010.03.12 19:49). Recently I'm hitting MetaPost capacity limit on expansion depth:

!mplib : mp terminal: ! MetaPost capacity exceeded, sorry [expansion depth=10000].

Increasing expand_depth in texmf.cnf and regenerating formats with context --make doesn't help. expansion depth is still at 10000 in error message.

texmf.cnf in texmf-local I've changed is reported by context as first one in log line starting with "mkiv lua stats : used config path"

What am I missing?

Michal