Default After backup in cwm internal storage unmounted

Hello and namaste everybody.. plz help me..
I have rooted p780 8gb with stock s124 rom.. yesterday i had backup my stock roms backup in cwm.. after backup and without make any changes or wiping anything i restarted my cell..
after restart cell boot normaly... but my internal storage partition was hide.. don't showing internal partition in file explorer.. only showing my 16gb sd card.. after some searching i mount my internal storage and now its showing...
But why that's happened.. i have been not chnges any option or wiping in cwm..
So any mastermind plzh help me why that's happened... and tell me wich is good recovery for my 8gb p780 for stock roms backup and restoration..
Thanx in advance
(Sorry for my bad English )

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