When a window is created from custom menu item, and a progress bar is generated through that window, if the user closes the window before the count down finishes on the progress bar, the menu item becomes unavailable on the menu.

Repro:
1. Download and open attached project
2. In menu bar, Example -> Progress Bar Usage
3. In the window appeared, click Display Bar button.
4. Progress bar window appears and starts to count down.
5. Before the Progress bar finishes, close the custom window.
6. The progress bar starts counting down and stuck (this is normal)
7. Try to reopen the window again via menu bar, Example -> Progress Bar Usage

Expected: The user can open the custom window after closing it before the count down finishes in progress bar
Actual: The menu item becomes inactive if user closes the window before the progress bar finishes counting down

Found in: 2019.1.0a11