The config dialog no longer has an apply or cancel button, which is inconsistent with, for instance, the filters dialog (bu there the cancel button doesn't work). Some settings, like fonts are applied automatically, but other settings, like show fave folder box or custom colors are not applied. The settings are shown as set by the user in the dialog, though.
kmail configure dialog has a apply/ok/cancel. Please create a screenshot but for sure we have it. Regards
After an update and reboot, the buttons are back...