I have a similar issue that's not resolved by maximising the main SoapUI window.
I'm using SoapUI 4.6.2 on OSX 10.8.5 (MacBook Pro, Retina, 15-inch, Early 2013). The problem also happened in SoapUI 4.6.1.
In SoapUI, under Projects->My Project->My TestSuite->My TestCase->Test Steps, I've created a REST Test Request entry. If I double-click this to open the editor window, the Request payload editor does not render the text properly; extra spaces are shown in the text (almost as if in places, tab characters have been expanded to spaces) and there's an alignment issue in that as one moves the cursor along a line, its placement creeps over the top of characters (it appears over characters instead of being placed in between them). The net result is that editing text feels very unreliable.
I'm running a second monitor (non retina) and if I move SoapUI onto this screen everything works OK.
Is there something in SoapUI's settings I can tweak to workaround this? I've tried disconnecting the second monitor and restarting SoapUI, but it still behaves the same way. I've been upgrading from previous versions of SoapUI on this machine, I don't know if that could be a cause; I haven't had time to try a full remove, cleanup and reinstall.
Any help much appreciated.
Regards,
Dave