I'm not able to save posts with cloned meta box groups. Only posts with extisting cloned groups with data already in it have this problem, not on newly created post. The error message is a frontend javascript validation error i think (request is blocked before submit). It says "Use the requested format" on top of the screen.
Ok, i've fixed it. Empty colorpickers were filled with the value # as a default. De error notification is on top of the screen instead of near the field, so when i turned off javascript the error was placed right under the input field of the color picker.
An update in the plugin has caused this problem. Maybe its good to create a fix for it. Its a fix for people using the plugin over serveral updates i think.
I've just tried a cloneable group with a color field and doesn't see that bug. Also, the code to remove the default '#' is added to Meta Box quite a long time ago. Can you give me more details on that? How did you setup the meta boxes?
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