An exception is raised when I start a cache: java.lang.NoClassDefFoundError: org/infinispan/config/PluggableConfigurationComponent.
It was worked fine with CR3.
I ran strings against compiled JdbcStringBasedCacheStoreConfig.class:

• CR3:
  $ strings JdbcStringBasedCacheStoreConfig.class | grep -i configuration
  =()Lorg/infinispan/config/AbstractNamedCacheConfigurationBean;
  9()Lorg/infinispan/config/CloneableConfigurationComponent;

• CR4:
  $ strings JdbcStringBasedCacheStoreConfig.class | grep -i configuration
  9()Lorg/infinispan/config/PluggableConfigurationComponent;
  =()Lorg/infinispan/config/AbstractNamedCacheConfigurationBean;
  9()Lorg/infinispan/config/CloneableConfigurationComponent;

Please note I used precompiled packages downloaded from sourceforge.net: infinispan-4.2.1.CR4-bin.zip and infinispan-4.2.1.CR4-all.zip.
There exists workaround: there is no issue when modules/jdbc is compiled from source distribution.