Vista - Can't read appSettings of IE hosted control when under SSL

I have the following issue.

..NET Windows Forms control hosted in the Internet Explorer cannot read
application settings from the configuration file when page is accessed over
SSL (https://localhost/default.aspx). Works fine when accessed using
"http://".

In both cases control itself loads and works fine.

Here are related code fragments:
---cut---file:default.aspx---
......
<!-- Configuration -->
<link rel="configuration" href="MyControl.DLL.CONFIG">
......
<object id="MyControl" classid="https://localhost/MyControl.DLL#MyControl">
......
---cut---file:MyControl.cs---
// Doesn't matter if ConfigurationManager.AppSettings are used instead.
string[] allKeys = ConfigurationSettings.AppSettings.AllKeys;
---cut---file:MyControl.DLL.CONFIG---
<configuration>
<appSettings>
<add key="MyKey" value="MyValue"/>
</appSettings>
</configuration>
---cut---

allKeys returns empty if page is accessed using "https://", otherwise keys
are in place as expected.

Environment: Windows XP SP2, .NET 2.0, Internet Explorer 6.0, IIS 5.1,
Self-signed SSL certificate, VS2005