Comment 9 for bug 1078695

For the record, and for anyone who might be googling:

I just ran across the same problem on Debian Wheezy Netinst running on a KVM virtual machine. The issue was that KVM's default emulated video hardware is Cirrus, which is very old and limited in functionality. I changed it on virt-manager to QXL (VM configuration, "Video" item, choose "QXL" on the drop-down list), installed the QXL X driver, and now I can use any resolution I want.