Why does my hilitedIcon stop flashing?

[Graham]

I created a square button and chose its hilitedIcon to be one of the 
standard icons - the little flashing alarm triangle. I hilited the button 
from the message box and it flashed for a bit then stopped. I can't see why 
- nothing I can find in the docs. The other moving icons seem to work OK. 
Obviously I can make my own animated GIF, but maybe I'm doing something 
wrong - has anyone else seen this?

Graham

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Graham Samuel / The Living Fossil Co. / UK & France