[Dridzt]

My local copy looks like this

local MOUNTERRORS = {
  [SPELL_FAILED_NOT_MOUNTED] = true,
  [ERR_NOT_WHILE_MOUNTED] = true,
  [ERR_ATTACK_MOUNTED] = true,
  [ERR_TAXIPLAYERALREADYMOUNTED] = true,
  [SPELL_FAILED_NOT_FLYING] = true,
  [ERR_PETBATTLE_NOT_WHILE_FLYING] = true,
}
local f=CreateFrame("frame")
f.OnEvent=function(self,event,...)
  if not MOUNTERRORS[...] then return end -- not an error message we care about, return immediately.
  if IsFlying() and not GetCVarBool("autoDismountFlying") then return end -- we are flying and don't have flight auto-dismount option checked, do nothing.
  Dismount()
end
f:RegisterEvent("UI_ERROR_MESSAGE")
f:SetScript("OnEvent",f.OnEvent)

(had submitted a patch along these lines long time ago but wasn't accepted so ... )

The issue with the sha voidzones is a bug with Blizzard and trying to apply Overcome by Anger on the player as if the player themselves are casting it.
This has a location trigger (like the auto-pickup quest functionality) but is applied as a texture debuff (same as "rested" can be applied to a map texture).

My suggestion would be to use the first version I posted and simply uncheck "Auto Dismount in Flight" from Interface Options -> Controls.

If you absolutely must keep that checked and want to suppress the dismount in this particular occasion,
this code will not win any beauty contests but will do the job.

local MOUNTERRORS,supress = {
  [SPELL_FAILED_NOT_MOUNTED] = true,
  [ERR_NOT_WHILE_MOUNTED] = true,
  [ERR_ATTACK_MOUNTED] = true,
  [ERR_TAXIPLAYERALREADYMOUNTED] = true,
  [SPELL_FAILED_NOT_FLYING] = true,
  [ERR_PETBATTLE_NOT_WHILE_FLYING] = true,
}
local f=CreateFrame("frame")
f.OnUpdate=function(self,elapsed)
  if supress then 
    supress=nil 
    f:SetScript("OnUpdate",nil) 
    return 
  end
  Dismount()
  f:SetScript("OnUpdate",nil)
end
f.OnEvent=function(self,event,...)
  if event=="UNIT_SPELLCAST_FAILED" then
    local _,_,_,_,id = ...
    if id == 129356 or id == 110668 then -- Overcome by Anger, or Fleet Winds
      supress = IsMounted() or IsFlying()
    end
  end
  if not MOUNTERRORS[...] then return end -- not an error message we care about, return immediately.
  if IsFlying() and not GetCVarBool("autoDismountFlying") then return end -- we are flying and don't have flight auto-dismount option checked, do nothing.
  if supress then supress = nil return end -- one time suppression for sha voidzones/smoke circles, and since we're not sure of the order of events do it both ways.
  f:SetScript("OnUpdate",f.OnUpdate) -- dismount on next frame
end
f:RegisterEvent("UI_ERROR_MESSAGE")
f:RegisterUnitEvent("UNIT_SPELLCAST_FAILED","player")
f:SetScript("OnEvent",f.OnEvent)