On SalesLogix pre-6.2 systems, the address Description was not considered when comparing Account and Contact addresses for the purpose of propagating a changed Account address to a matching Contact address. However, with 6.2 and above, if the Address Descriptions do not match, the addresses are not considered a match. Because the Account address Description and the Contact address Description fields use different picklists, the odds that descriptions do not match is pretty high.
The only workaround is to remove the Description Criteria from the System:Add Edit Address form script. If you are continually updating Contacts with the most recent Account Address you may want to make this change. The Web client did not display the same behavior so if you are only using the web client there is not need to make the script changes.