Hello Sven,
Yes this is a known restriction in our system (well observed). Technically it is not a lookback problem but more if what is known as a spiral problem.
As part of the re-development of our new call forwading system we must overcome this exact situation, so you can expect things will work for you once this new enhancement is relased.
Edit: This problem has addressed as part of the latest release. See
http://forum.voxalot.com/showthread.php?t=1119