http://www.tski.co.jp/baldio/patch/20010109.html January '01. ~1month after Velious.
"Root-type spells and 'snare' type spells now use a separate spell effect.
Previously, 'Root' spells would overwrite any snare effect upon the target. When the root would wear off, the target began moving at full speed. With this change, when root wears off, snare will still be in effect. This has a few added effects on the other end.
For instance, root will no longer cancel SoW or Journeyman's Boots effects. It also allowed us to correct a long-standing bug that was allowing bards to cancel root on themselves by playing Selo's Accelerando if Selo's was in effect at the time that the bard was rooted. As mentioned in a previous patch where the first part of this bug was fixed, this was not the intended effect."
BTW, if a dev reads this. Root should be overwriting SoW/Jboots & Selos (Although if a bard casts selos again they should be able to overwrite the root with selos).