What happened - Windows 7 64b - reproduces on 5.3.3p2 and 5.4.0b8
When you start Server and Client in Standalones and connect them - then when you closing Client's Standalone window (by red cross in left upper corner of the window) - it crashes

How we can reproduce it using the example you attached

--- please see attached video ("StandaloneCrash.swf") ---
1 Open attached project
2 Build Standalone and start 2 or 3 instances
3 In first Standalone Create Internet Match (or LAN Host)
4 in second (or second and third) Standalones make "Find Internet Match"->Connect (or Lan Client)
5 Close second Standalone (with Client) window using window control (red cross)
Actual result: Standalone crashes

- there is log in project folder in "3_Data"->"output_log.txt" from crashed Standalone (but seems it has nothing interesting)