Clamp and update every timestep is broken BADLY

Edit/ Settings/ General/ Clamp and update every timestep is badly broken. Earlier today, I got it to work on a Windows box, then could not turn it off. I had to delete the config files! Just now with OS X, I can't get it to turn on.

Mac (and Windows), 5.5.0, built-in server.
Open can.exo. All vars on. Apply. Paint by ACCL.
Change Grow and Update on 'Apply' to Clamp and update every timestep. OK.
Play Min and max for the color legend won't update!

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