Cannot have more than one Design Studio's open at a time

Steps to reproduce:

• Install latest Design Studio 4.6 snapshot
• Start Design Studio
• -> Opens correctly
• Start another instance of Design Studio
• -> Does not open, but in task manager I can see there are two Design Studio's running. Still only one is open.
• Close Design Studio and wait for a while
• -> now the second Design Studio instance opens

This behaviour has changed quite recently: E.g. build#175 from 15th August still opens both Design Studio's, but latest snapshots have this "one-at-a-time" behaviour.