yes we know, somebody discussed here these "features" from

but it could be useful, to give a complete and good description

of these features available in the actual Max/msp-version

yes we know, somebody discussed here these "features" from
former Max/msp-versions 

but it could be useful, to give a complete and good description
of these features available in the actual Max/msp-version

how-to-avoiding-round-corners-in-externals-numboxes-commentboxes-etc

Comments do not have rounded corners. For numberboxes use [live.numbox]. Some GUI objects, like [panel] or [umenu] have "Roud-ness of Box Corner" parameter (in Inspector) - set the param to 0.

Unfortunately I have no tips for messageboxes and objects/externals.

how to avoiding round corners in externals, numboxes, commentboxes etc.