Modal window can't close if opened in two browsers

Hello colleagues,

I am having a modal window which when opened in two browsers, can't be closed in the first one. It can be closed in the second, but still exists in the first, although the context gets cleared and obviously the methods for close are called. When I try to close it again in the first browser, the corresponding methods are still called, but nothing happens on the UI - the modal window just stays there.

Here are the open and close methods of the window:

Could you please tell me if this is a bug, or what I shall implement in addition in order to avoid the problem?

Thank you and regards,

LL