Your observation is both true and false
By inheriting a Visual WebGui control, you are inheriting two inter-connected, but different parts of the control.
First is the server-side part, the one you program in C# or VB.NET. This part is not affected by the setting or not setting the MetaDataTab.
Second, there are the client resources part, which includes the XSLT, JS, CSS etc. It is in the XSLT transformations where the MetaDataTag matters.
So, Including a MetaDataTag setting, as you did in your problematic version of the control, you are inheriting the server-side code (the C# and VB.NET), but as you did change the MetaDataTag, but didn't supply any XSLT to handle that new tag, no Html code is created when your control is rendered to the browser. That's why I say it's both true and false.
Hope this explains,