I've encountered this a few times in the past and it seems to happen when I leave the save as dialog open for a few seconds and tab to another application. I wasn't interacting at all with the save as dialog and during this latest instance I was typing in an IM application called trillian while the following errors came up. Hope this helps!
Program timeout (infinite loop?) Called from local function #3703 (hxd/System.hl.hx line 388)
Called from hl.$UI.chooseFile (C:\projects\haxetools\haxe\std/hl/UI.hx line 209)
Called from hl.$UI.saveFile (C:\projects\haxetools\haxe\std/hl/UI.hx line 172)
Called from hxd.$File.saveAs (hxd/File.hx line 217)
Called from Client.~onSaveAs.0 (Client.hx line 1178)
Called from dn.Delayer.update (dn/Delayer.hx line 106)
Called from dn.$Process._update (dn/Process.hx line 257)
Called from dn.$Process._update (dn/Process.hx line 269)
Called from dn.$Process.updateAll (dn/Process.hx line 223)
Called from Boot.update (Boot.hx line 72)
Called from hxd.App.mainLoop (hxd/App.hx line 187)
Called from hxd.$System.mainLoop (hxd/System.hl.hx line 70)
Called from hxd.$System.runMainLoop (hxd/System.hl.hx line 135)
Called from hxd.$System.runMainLoop (hxd/System.hl.hx line 132)
Called from haxe.$Timer.~delay.0 (C:\projects\haxetools\haxe\std/haxe/Timer.hx line 143)
Called from haxe.$Timer.~__constructor__.0 (C:\projects\haxetools\haxe\std/haxe/Timer.hx line 76)
Called from haxe.$MainLoop.tick (C:\projects\haxetools\haxe\std/haxe/MainLoop.hx line 174)
Called from haxe.$EntryPoint.processEvents (C:\projects\haxetools\haxe\std/haxe/EntryPoint.hx line 99)
Called from haxe.$EntryPoint.run (C:\projects\haxetools\haxe\std/haxe/EntryPoint.hx line 125)