Description of problem:
All of these source viewers are affected: ERDF, JSON, BPMN2, SVG. When a viewer is open for the first time it works fine and it can be closed. When it is open again it's broken. It displays ok, but it cannot be closed using the Close button or the X button in the top-right corner.

Version-Release number of selected component (if applicable):
ER6

How reproducible:


Steps to Reproduce:
1. go to designer (open a BPMN2 process)
2. click on of [ERDF, JSON, BPMN2, SVG] buttons and close the window
3. click the same button again and try closing the window
  
Actual results:
The window doesn't disappear.

Expected results:
The window should close and it should be possible to open it again and work with it repeatedly.

Additional info: