Use same strWindowName for window.open(), but still popup more new windows.

I use window.open(strUrl,strWindowName) to popup windows.
When a window with the name strWindowName already exists, it is expected that even another invoke on the same window.open will just use the same window already opened.
But I found when the strUrl is in HTTPS, Opera will always popup new windows, while for strUrl in HTTP, Opera will just refresh the previous popup window as expected.
In other browsers, it works well, Could you tell me why Opera is acting differently when the strUrl is in HTTPS?
Thanks a lot.