"Auto Checkin Nodes" is activated (i.e. true). Hence I would expect that when I modify (a property) of my mixin:versionable node, a new version is created. Unfortunately this is not the case.
Looking at AbstractSlingPostOperation#run only CREATE, CHECKOUT or CHECKIN "trigger" a potential checkin, but not MODIFY. Shouldn't we?: ... case MODIFY : response.onModified(change.getSource()); if ( versionableConfiguration.isAutoCheckin() ) { nodesToCheckin.add(change.getSource()); } break; ... maybe additionally check whether the node is really checked out? WDYT?