Object-oriented techniques like inheritance promise great benefits for the specification and design of parallel hardware systems. The difficulties which arise from the use of inheritance in parallel hardware systems are analyzed in this article. Similar difficulties are well known in concurrent object-oriented programming as inheritance anomaly but are not yet investigated in object-oriented hardware design. A solution how to successfully deal with the anomaly is presented for a type based object-oriented extension to VHDL. Its basic idea is to separate the synchronization code (protocol specification) and the actual behavior of a method. Method guards which allow a method to execute if a guard expression evaluates to true are proposed to model synchronization constraints. It is shown how to implement a suitable re-schedule mechanism for methods as part of the synchronization code to handle the case that a guard expression is evaluated to false.