Ah Ok.

Kakashi developing the MS at such an early age does kind of throw his development off a bit. Having such an ability yet going through such dangerous situations as the fight with Zabuza, Orochimaru and of course Itachi without zapping them away in to another dimension whilst risking life and limb is a bit hard to explain away. The only reason I can think of is that he felt his MS was a result of killing Rin and as that was something he hated he didn't want to benefit from having committed such an awful action. However when it came to fighting Itachi he realised the only the way to defeat him and Akatsuki was to use MS which why he began to train using Kamui.