Fabric 6.x: "io.fabric8.api.FabricException: Could not find port within range [8501,8544] for pid org.ops4j.pax.web"

Issue

We utilize the Fabric Port Service to allow services like Pax Web to start up on a free port within a specified range. E.g. we configure

profile-edit --pid org.ops4j.pax.web/org.osgi.service.http.port='${port:8501,8544}' fabric

However when provisioning a new container with this profile we are getting this error

io.fabric8.api.FabricException: Could not find port within range [8501,8544] for pid org.ops4j.pax.web

despite free ports being available in the specified range.