Since some weeks I have strange problems with MetaPost in MKIV (beta). The
attached example should (and did in the past) output a central box ("Fakt")
surrounded by five boxes named "Dimension". However some of them (in that
particular example one) is drawn wrong: the box is on the right spot, but
the label seems to be at 0,0. It seems to happen whenever the boxes are
drawn from within a loop - at least all of my problems with boxes show
similar symptoms and only occur within loops.

Any ideas what goes wrong here?