Hi,
I cannot comment on your problem, about disabled account, but yes WEB VPN password change doesn't work on VPNC 4.7,
http://www.cisco.com/en/US/products/hw/vpndevc/ps2284/products_configuration_guide_chapter09186a00803ee122.html#wp1008820
"In this release WebVPN does not support RADIUS with Expiry authentication."
About your caching kind of problem, can you double check that you are not disabling account on secondary domain controller, as it wont replicate the settings till next replication cycle(I guess). Ensure that.
With ASA, Web VPN password change might work. Have to look into doc.
Will let you know if I find something.
Regards,
Prem