Workbook specific ribbon disabled

I am using a workbook specific custom UI which generally works OK however...

Following from a previous post I am defining
       Global gRibbonUI As IRibbonUI
then using
        gRibbonUI.Invalidate
to re-evaluate the custom tab after different processes are executed.
However I'm finding some oddities - no comments about 2007 being one of those oddities

Anything using a getVisible or getEnabled is rebuilt correctly after the Invalidate command. I'm using this to control the options available depending on flags within the workbook.
Anything using a dynamic dropdown does not get rebuilt.
If I do a save as then the custom ribbon tab is completely disabled unless I close the workbook and re-open it. The main ribbon is fine, it's only the custom bit that dies.
     Unless, that is, the custom ribbon tab is the active tab when doing the 'save as'?!?

Any hints or has anyone overcome the rather annoying 'Save As' = 'disabled ribbon' problem.

Thanks