Simulations run in a separate process now. This has the advantage that MLDesigner no longer crashes due to programmer error in user defined primitives. This comes along with a couple of changes.
A Debugger Mode was added to debug user defined primitives with an external debugger. You can choose between a text based debugger (gdb) and a graphical debugger (ddd) in the Settings (Run Control→Debugging).
On Windows, the only supported debugger at the moment is gdb.
You can enter the Debugger Mode by a click on the arrow next to the toolbar button Switch to Simulation Mode and choose Switch to Debugger Mode.