We recently purchased some 3Com IntelliJack NJ225 switches:
The specification states that they support IEEE 802.1D, and a mandatory part of this standard is support for the rapid spanning tree protocol. However, we quickly realised that we could not safely create loops when connecting these devices together (using the four "front" ports). After several support calls, 3Com confirmed that they did not implement the RSTP.
I think it's fair to say that we're not using these switches for their intended purpose. But, did 3Com incorrectly claim support for IEEE 802.1D? Or is there a technical reason why these switches are exempt from implementing the RSTP?