http://www.eqclerics.org/forums/showthread.php?t=10980
"Slow is the key to klandicar, give a bard a tash stick - due to the way that bard songs stack enchanter cast tash and tash from a bard wielding a tash stick both stack."
This patch possibly changed it...
May 30, 2001
** Spell and Song Changes and Bug Fixes **
- We've been fixing holes in the spell stacking code. For the most part
the changes fix bugs that allowed tricks to get spells to stack that
were never intended to stack.
This is definitely a classic mechanic and should be added. That extra tash makes a huge difference trying to slow velious mobs. And the lava diamond stacking adds a ton of dps when slow isn't viable.