I have the same configuration (Streak + mxHero).
And sometimes the same problem with the layout and view of the window. No mxHero button.
Comes back by reloading the whole window or closing the email and opening from the Draft folder again.

Got this exact message 3 or 4 times.

HI! Congratulations on your great producto! Really helpful and extremely reliable. Keep up the great work guys!

Regarding this specific issue: my white screen currently lasts about 3 to 4 seconds. And after this I get an OK button (which I must click to continue).
I think this OK button might be changed to a message, a non modal or non mandatory message to click. To an informative message Gmail styles rather than the current mandatory click OK.

Thanks!
Fede.