It may happens, for several different reasons, that the "Loading..." frame never disappears, leaving everything behind it obfuscated and non-clickable.
For example, if the Business Process Designer was left open with a process containing some errors, the 'x' on the top right corner cannot be clicked, therefore everything remains blocked and unusable, forcing the user to refresh the whole page.
It could be useful to leave focusable some parts of the interface, like the 'x' buttons.