We can regret that HP has not be aware of this issue
into repeated a lot into various forum by unsatisfied users.
I reckon HP would be fully aware. When I installed Windows 7 a year ago, I contacted HP to enquire about the Scanjet 4800 series, which has the same problem as the 4600 series. The driver is available and enables basic scanning, but
the driver doesn't enable scanning of slides and other special functions. That requires other HP software that comes with specific scanners and HP told me they had no intention of releasing a 4800 series software update for Windows 7.
So I uninstalled everything HP and purchased a Canon CanoScan 5600F and was delighted to discover that it does a much better job than the HP ever did, and does it easier. I won't be going back to HP anytime soon!