I concur with dennis,
The installer formats /home partition despite the partition format checkbox unchecked.
Loss of data is unavoidable
This is rather strange because Unity uses the installer from mandrake/KDE
The installer also (re)set a BIOS option
It turned the power to my optical PS2 mouse off
To repair this, I needed to physicaly reset the motherboard (restrep)
(which was a waaay back old bug in the mandriva installer)
You might need to supply a better and correct installer/formatter from mandrake/KDE

Greets, Arend.