FULL PRODUCT VERSION :
java version "1.6.0"
Java(TM) SE Runtime Environment (build 1.6.0-b105)
Java HotSpot(TM) Client VM (build 1.6.0-b105, mixed mode, sharing)

ADDITIONAL OS VERSION INFORMATION :
Windows XP Professional Version 2002 SP2

A DESCRIPTION OF THE PROBLEM :
If the update policy is set to "prompt-update" Webstart is always prompting the user reporting available optional updates. Regardless wether there are updates or not.
This is happening even if the network is down (with <offline-allowed/>) where Webstart has not chance at all to compare its cached resources with the resources available on Server.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
include the tag
<update check="always" policy="prompt-update"/>,
<update check="timeout" policy="prompt-update"/> or
<update check="background" policy="prompt-update"/>
in the .jnlp and start the application multiple times without updating the resources on server.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Webstart should compare timestamps or version information returned from server against the ones of its chached resources and only prompt the user for an application update if at least one resource on server is newer than its cached version.
ACTUAL -
Webstart always reports available updates and prompts the user to download even if it has no chance to do any comparision because the server is down.

REPRODUCIBILITY :
This bug can be reproduced always.

CUSTOMER SUBMITTED WORKAROUND :
No known workaround.