I believe this might be a bug introduced in 3dsmax 2020 or 2021. The code below works in version 2019:
customFlags = attributes custFlags attribID:#(0x281c9c82, 0x33ddf1b5) ( parameters params rollout:controls ( value type:#integer default:123 ) rollout controls "Flags" ( button reset "Reset" fn Update = ( print value ) on reset pressed do ( Update() ) on controls open do ( Update() RegisterTimeCallback Update ) on controls close do ( UnregisterTimeCallback Update ) ) ) cube = Box() custAttributes.add cube customFlags
What it’s doing doesn’t make much sense, of course. But the problem is that the Time Change callback will fail in Max 2021, whereas it works in 2019 and earlier versions. (I didn’t have a chance to test it in 2020).
See the screengrab for details:
Does anyone have experienced this? Is there a workaround?
And if this is a bug indeed, how do I report it to Autodesk, so they can actually consider this for a fix?