HTML href not working

I am hoping that I've just made a simple mistake on what should be a very simple bit of HTML. The issue is that this below example the frame targets work for "main.php", "phpinfo.php" and "awstats/awstats.pl?config=Stormwind". However, the links "https://stormwind:10000" and "phpmyadmin/index.php" insist on opening in a new window. Am I just missing something?

<ul>
<li><a href="main.php" target="main_window">Home</a></li>
<li><a href="https://stormwind:10000" target="main_window">Webmin</a>    </li>
<li><a href="phpmyadmin/index.php" target="main_window">PHP MyAdmin</a></li>
<li><a href="phpinfo.php" target="main_window">PHP Info</a></li>
<li><a href="awstats/awstats.pl?config=Stormwind" target="main_window">Awstats</a></li>
<li style="float:right"><a class="active" href="#about" target="main_window">About</a></li>
</ul>
<base target="main_window">
<iframe src="main.php" height="100%" width="100%" name="main_window">      </iframe>
</body>
</html>