Just to point out.. This is working as intended according to blizzard themself..
I quote
Edit: Source = http://www.wow-europe.com/en/info/fa...ange/index.xml under the ''Other'' sectionQuests
All currently active quests will be removed from the character's quest log. Faction-specific quests will be removed from the character's completed quest list, as well as any faction-neutral quest that is part of a quest chain. Standalone faction-neutral quests will remain in the character's completed quest list. The opposite-faction version of a faction-specific questline is available in its entirety after a faction change.