gitflow-maven-plugin: When starting new release "Release branch already exists. Cannot start release."

When starting new release with mvn gitflow:release-start I receive an exception because of old-release branch… “Release branch already exists. Cannot start release.” In fact, plugin refuses to create branch “release/1.0.1” because there is branch “release/1.0.0” already existing. What is the correct workflow in case there are many installations of the product with different release versions so all release branches should be maintained? I use <keepBranch>true</keepBranch> because of that. However it causes this exception… Btw. how is it possible to set <keepBranch>true</keepBranch> only for release, release-start and release-finish goals and keep it false for other goals in parent pom? It seems like goal release doesn’t create release branch. It would be nice if it did in case keepBranch=true.