This seems to be a Virtualbox problem: I just installed DragonFly 3.6.2 anew on Virtualbox 4.3.10 and ran into the same problem. The other DFly 3.6.2 image that I am using and that runs fine was installed using an older version of Virtualbox (perhaps 4.2.x); I should revert back to that one.
Okay, interesting at least. :) Sascha