VS2010: Why do my custom Toolbox tabs and contained controls keep disappearing?

This is how I expected the toolbox to work:

Let's say I add a custom Tab to the Toolbox called "Ajaxtoolkit." To add controls to the new tab, I right mouse click and select "Choose Items" and browse to a file, Ajaxtoolkit.dll, that is of a particular version number.

I would expect that when I save and reopen the solution, that the Ajax Toolkit custom tab would still be in my Toolbox and that it would contain the same controls that were there last time, the controls that were in the dll that I referenced when the controls were added.

If I created a brand new web app, I (possibly) wouldn't expect to see the same Ajax Toolkit custom tab. However, I could perform the same steps as above and add a "Ajax Toolkit" tab and perhaps, this time, select a DIFFERENT VERSION of the tookit, and the state 开发者_JS百科of the toolkit would be retained with each solution file.

Another possibility would be for the original Ajaxtoolkit to be retained when the 2nd web solution is created, and perhaps, if I wanted to mix versions of the toolkit across diffreent web sites in my solution, I should start naming my custom toolkit tabs with version specific names like "Ajaxtoolkit 4.0," etc.

...But instead, the Ajaxtoolkit tab disappears when I close VS2010 and reopen it.

Why? Is this desirable behavior or a bug?

You know VS2010 is a fully customizable IDE, may be these features conflicts your toolbox customization.