Below is a minimal not-working example extracted from "extensions-001.tex" in the fonts section of the test suite. From what I understand of the code, the second line should read "XPrXcXdXPrX" instead of "abracadabra". But it doesn't, it is still "abracadabra". Compiling the original extensions-001 gives me seven lines of "abracadabra". What am I doing wrong? I'm running ConTeXt version 2015.05.18 12:26 MKIV current fmt: 2016.4.28 from the debian/ubuntu texlive packets.