window.open why some user's IE open new window every time.

This issue is driving me crazy, I have an app which is referenced via .asp pages and in one of these pages there is a javascript function to open a popup

window.open("popup.aspx", "myPopup","width=300,height=100,status=no,toolbar=no,menubar=no,scrollbars=no,resizable=no,alwaysLowered=yes,location=no,directories=no,titlebar=no");

Looking up various documentation it has been stated that if the same window name is used then this window will be re-used. This is correct on most user's IE but on an some end users PC it opens an additional popup window even though the same code is being used.

To verify this I created a test.aspx and simply duplicated the open function previously stated. On my PC I got one popup window, on the some users got two. It’s definitely Internet Explorer on this PC because I have installed Firefox and there is no issue and the same window is referenced. IE(11) version is same all.

What problem??