diff --git a/IPython/shellglobals.py b/IPython/shellglobals.py
index 7b69bec..48994bf 100644
--- a/IPython/shellglobals.py
+++ b/IPython/shellglobals.py
@@ -80,3 +80,17 @@ else:
         Term.cout.flush()
         # Set global flag so that runsource can know that Ctrl-C was hit
         KBINT = True
+
+def run_in_frontend(src):
+    """ Check if source snippet can be run in the REPL thread, as opposed to GUI mainloop
+    
+    (to prevent unnecessary hanging of mainloop).  
+    
+    """
+    
+    if src.startswith('_ip.system(') and not '\n' in src:
+        return True
+    return False
+    
+    
+    
diff --git a/IPython/twshell.py b/IPython/twshell.py
index 1a5e444..d0c2696 100644
--- a/IPython/twshell.py
+++ b/IPython/twshell.py
@@ -105,7 +105,7 @@ class TwistedInteractiveShell(InteractiveShell):
         # in IPython construction)
         
         if (not self.reactor_started or (self.worker_ident is None and not self.first_run) 
-            or self.worker_ident == thread.get_ident()):
+            or self.worker_ident == thread.get_ident() or shellglobals.run_in_frontend(source)):
             InteractiveShell.runcode(self,code)
             return