Either Kabob or Kabab are still acceptable, even though spellcheck doesn't agree.

Depends upon country of origin, who translated the word into English, etc. It will probably be standardized eventually, but hasn't happened quite yet. And then it could be changed again someday.
Sort of like Peking vs Beijing - it was translated and spelled the way it
sounded to early English speaking visitors, then corrected to the actual Chinese later.