O.k. some findings:

-Setting the resulotion higher than 600 will fail
-Changing color-mode seems to have no effect
-after initial scan some new color-modes are added
-GUI is unresponsive while scanning
-SCANdal does not return when I plug in my scanner after I clicked "scan" (yeah stupid me, should still not hang)
-clicking "process" with no plugin selected will make SCANdal meditate, a simple safety-check should help here.