Designer file not updating in certain scenarios...

I have an assembly full of custom web controls which preferably I would like to
globally register for the whole web application to use.  I have done this in the
usual way within web.config and all the pages can reference and use these
controls, great.  However, the designer file does not update when I add new
controls to the form unless I register the custom controls assembly on the page
itself.  The moment I do that, the designer file becomes back in sync and
everything works fine.  Strangely enough, for some user controls I don't
actually have to do this and the designer file still updates.  Every page
requires it though and this is not ideal because it removes the ability to
globally reference a single assembly.

 I am presuming that there is a solution to this, I just don't know what it is. 
Any ideas?

I'm experiencing the same problem here. Were you able to find a resolution to
this problem yet?