I don't know if this occurred before the patch, but there seems to be a bug with these 2 skills if both are stacked:
Cast shadow armor, then shadow bowman, and you'll receive shadow armor's block permanently.
To remove this bonus block, wait for shadow bowman to expire and cast shadow armor. Once shadow armor expires, so does the bonus block.
Another issue is reapplying shadow armor. If you cast it, then recast it before it expires, the block bonus timer will NOT reset, but the floating model timer above your character WILL. In other words you have no idea when your block rate will diminish, which is almost suicide in HC. An immediate "half-fix" for this is maxing the passive block skill then putting enough points into shadow armor to hit 50% block. An easy way to fix this would be to simply add a visible timer to shadow armor to prevent recasts until that timer expires, just like haste.
And finally a request,
When playing HC, I buff myself with the following: spectral echo, haste, frost shield, shadow armor, elemental protection, entropic aura. I've learned to live with spamming buffs every 20-30 seconds, but I play a destroyer, not a... badass bard.
