I have version control configured to use the Perforce command line system on 64 bit (in the absence of the 64 bit SCC provider DLL), with "Auto check-out on edit" enabled.
When I edit a read-only file that will need to be checkout out, I get the dialog with the option to "Check out the latest version", but when I click "OK", VS runs a "p4 sync <my file>" command rather than the "p4 edit <my file>" required to do a checkout.
Checking out the file manually from the "Version control->Checkout..." context menu runs a different set of commands and succeeds ("p4 -ztag fstat ..." twice, followed by "p4 edit").