To better explain what he's saying:
Dyed Armor contains a line of lore saying that it is dyed. HideFlags cannot currently hide this and it should be able to.
It seems that the chicken jockeys continuously spawn in more chickens, which begin laying eggs everywhere, which causes the zombies to pick them up, which causes pockets of persistent zombies who do not contribute to the mob cap. This generates much more lag than you would think because the server is loading in more hostile mobs than it should be.
The "Tile" NBT tag has no impact on what block spawns, and neither does the "Data" tag. The spawner will only spawn sand, regardless of whether it worked in previous versions or not. Backdating causes the spawner to work as normal.
This is actually quite buggy - if you use a map on Single Player that has a resources.zip in its folder and then log onto a server that has a map with resources.zip, the game will activate the pack from your single player map - and there's no way to disable it short of a client restart.