Sometimes when i slash and get a hit the block-sound is played. This also happens when the guy being slashed only stands on the spot without having a sword and hud attached (so it has nothing to do with blocking..) :-)
Can you tell us if it happens with all swords or only particular swords? This was an issue that we had thought we resolved recently, but it appears to have resurfaced. It's an easy fix, but in and of itself probably isn't worth a new update since updates in Second Life are harrowing and time-consuming.
This also seems to be one small part of the problem with "blocking bugs", since the sound is somewhat misleading, so it's definitely something we wish to address as soon as possible.