"mvn gwt:run" without clean no longer works

Until some time ago, it was possible to do "mvn gwt:run" on drools-wb-webapp and optaplanner-wb-webapp and take advantage of incremental calculation (which is a big speedup).
In a recent maven-gwt-plugin upgrade (not necessarily the last), this no longer works reliably with changes in kie-wb-common which did get a "mvn clean install".

To reproduce this:

• make a change in the client and server side of drools-wb and kie-wb-common
• build those artifacts without "clean" and do a "mvn gwt:run" of drools-wb-webapp