Unable to block Ring-bearer with creatures weaker than the Ring-bearer.

The card clearly states that becoming the Ring-bearer makes the card unblockable by creatures with greater power. There were no other card affects in place changing blocking rules, both my Hare Apparent and my rabbit token were untapped and able to block the Nazgul, but neither could be assigned to block the Ring-bearer (the Dokuchi Silencer).

I am new to arena, so if this is a known and accepted bug with content related to this LOTR stuff, please do let me know, and then explain why it is still legal to use content that is known to be broken and bugged.