#APL 29#

    {1↓¨(1,(⍳⍴⍵)∊,{1↑1↓⍵}⌸⍵)⊂1,⍵}

This is a nice question for the key operator (⌸) which was introduced with Dyalog APL v14.
It takes the left argument function ({1↑1↓⍵}) and gives it for each unique argument, the indices in the vector for that argument.
Here I'm taking the second index, then i check which of the indices is present in this list ((⍳⍴⍵)∊) and use the resulting boolean for splitting the original vector.

Can be tried online here:

[http://tryapl.org][1]


  [1]: http://tryapl.org/