During installation, when Anaconda is required to set up an network connection (e.g. when adding repositories), a DHCP dialog pops up. On that dialog is a check box labeled "Enable IPv4". It is very difficult to imagine that NOT enabling IPv4 could possibly be the right thing, and from memory I think this check box USED to be labeled "Enable IPv6". Further, I suspect strongly that what it actually *does* is enable IPv6. This is moderately confusing, and if I am correct that it is a typo I suggest adding a statement about it to the release notes ASAP.
What you are seeing is a simplication of the user interface that was present in previous releases. In F-10, we lack IPv6 support during installation. We disabled the IPv6 checkboxes and input fields, but when we gain IPv6 support again, we'll turn those back on. The dialog box does look a little strange, but it was done this way for minimal disruption to the UI code.
Understand IPv6 not present during install, but this still seems very very strange. Given that IPv6 is not present, what does it mean, exactly, for the user to attempt a network install and *disable* IPv4 support? Given what you say, I think this check box ought to be checked and *disabled* (i.e. user cannot uncheck) until IPv6 support is restored. Clearly not critical, but given that the option being presented to the user is complete nonsense it definitely IS a bug.