Tiger and Leopard clients have different MCX key for CreateAtLogin

I’m seeing an issue where Tiger clients prompt new network users to Create Mobile accounts (as expected), but Leopard 10.5.4 clients do not. We bind to AD for auth and OD (all computers are Guest) for policy. when i do a dscl to see the MCX, i see this:

Tiger cilent:

<key>com.apple.cachedaccounts.CreateAtLogin</key>
<true/>
<key>com.apple.cachedaccounts.WarnOnCreate</key>
<true/>

Leopard client:

<key>com.apple.cachedaccounts.CreateAtLogin</key>
<false/>
<key>com.apple.cachedaccounts.WarnOnCreate</key>
<true/>

Any thoughts as to why this is?