Patch 5.3.0 (20-May-2013): Glyph of Mass Dispel has been redesigned and no longer reduces cast time. The glyph now enables Mass Dispel to dispel magic effects that are normally undispellable.
/Patch 4.0.1 (12-Oct-2010): Changed from Reduces the mana cost of Mass Dispel by 35%.
Patch 3.1.2 (2009-05-19): Changed from Reduces the mana cost of Mass Dispel by 50%.
Hotfix (2009-04-28): "Glyph of Mass Dispel will now reduce the cost of the spell by only 35%. [1]"
Patch 3.1.0 (14-Apr-2009): Changed from Reduces the mana cost of Mass Dispel by 20%.