Fix failure of workflow task layout display

Steps to reproduce:
(Using Firefox; cannot be reproduced in Chrome)

• Create a custom workflow according to the Studio - Web UI Customization test scenario.
• Navigate to Designer and select the workflow from the layouts menu.
• From the main view, click on the workflow task.
  => Nothing shows in the main view.
• Switch to code view.
  => Nothing shows in the main view.

It seems that after a 2-3 minutes of waiting and/or switching back and forth between code view and "view" view, both pages display properly, however clicking on another layout (custom document type create layout, for example) reproduces the problem.