In Hibernate 4.2.4, Configuration.java, method generateSchemaUpdateScriptList(Dialect dialect, DatabaseMetadata databaseMetadata), line 1219 says:

String constraintDropString = uniqueKey.sqlDropString( dialect, tableCatalog, tableCatalog );

There is multiple times "tableCatalog" in argument, however we believe, the arguments should be: ... tableCatalog, tableSchema, as the documentation of sqlDropString says and as used everywhere around that place.
Unfortunatelly, we did not create environment in which we would test the case.