Correct this happens when host cache is enabled.
Details about host cachine is here http://communities.vmware.com/docs/DOC-19439
If you are constantly changing settings and working on the pool you may want to set a block out period, that way if it works the way I believe it does the digest should recompute during the blackout periods. Let me know how you go.
Blackout times
This defines recurring schedule for which the cache regeneration should not be performed. This option allows the administrator to plan the 'digest recompute' to run only during non-business hours, off-peak schedule etc. Refer figure 4. Here the cache regeneration is not performed during 9 AM to 6 PM on all week days
