Thanks for your bug report. Unfortunately I have not been able to reproduce this issue so far. When I test your link in mIRC v7.43 in any version of Windows, mIRC correctly opens the full URL including the #bookmark. If you open the mIRC/Options/IRC/Catcher dialog and enable the "Show warning when opening a URL", this will display a Link Warning dialog when you double-click on a URL and will display the URL that will be passed to your web browser. Do you see the full link in this dialog?