I need your help

I love peppermint bark and after making several unsuccessful attempts at homemade bark, I decided to turn to my blog followers to seek your advice. This seems like such an easy process and it frustrates me that I can't seem to get it right. 

I start with the three basic ingredients for peppermint bark - dark chocolate, white chocolate and peppermint.  I learned the hard way that crushing candy canes myself is both really messy and unproductive.  (I usually end up with either large chunks or peppermint dust.)

I melted my dark chocolate in the microwave.

I poured it into a parchment paper lined pan.

I let the chocolate cool and then I melted the white chocolate the same way and spread it over the dark chocolate.

While the chocolate was still warm, I sprinkled the crushed peppermint over the top.

I let the bark cool overnight.  I removed the bark from the pan by picking up the paper.

I used a chef's knife to cut the bark into pieces.

This is where the problem starts.  When I start to cut the bark, the dark and the white chocolate separates.  I ended up melting some more white chocolate and "glueing" the pieces back together.  Can anyone help me figure out how to keep the dark and white chocolate from separating?

OK blog friends, I am turning to you for advice.  If you have suggestions on how to keep my peppermint bark together, send me a comment.  Thank you.

Bon Appetit!