cluster drive letters changed

Hello All,

I have a two-node sql server(2012) cluster  on Windows server 2008 R2. There is 2 database resources in the cluster. I moved all my resources from node 2 to node 1 and restarted node node2. but suddenly 3 of drive letters which belong to db2 changed!! but I changed them back  manually. I can not find a specific cause for that!  any Ideas what it could be?

Thanks,

M