Hello, certain characters within the mplibcode environment (even in comments) make problems: < > tab (Perhaps there are still more.)
If you read the same MetaPost code via filecontents* or the MetaPost command input everything is fine. I've attached a minimal example. Observed on Windows XP with a fairly up-to-date TeX Live 2010 installation including the tlcontrib repository. Yours Rolf Dieterich
test-luamplib.ltx
Description: Binary data
