FULL PRODUCT VERSION :
1.8.0_31
1.8.0_40

ADDITIONAL OS VERSION INFORMATION :
Windows Vista
Windows 7 32 bits
Windows 7 64 bits
Windows 8

A DESCRIPTION OF THE PROBLEM :
We deploy a jar through a tomcat 6 running on java 6.
At the launch of jnlp, the application is downloaded regularly while the jar was not changed.
The dysfunction is present on several stations running on Windows Vista, 7 (32 or 64 bit) or Windows 8.
The problem has been reproduced with differents JMV versions (1.7.xx and 1.8.xx).

Jnlp used :
<?xml version="1.0" encoding="utf-8"?>
<jnlp spec="1.0+" codebase="http://server/common/installs/jws/">
<information locale="fr_FR">
<title>Module</title>
<vendor>Company</vendor>
<homepage href="http://www.company.com/"/>
<offline-allowed/>
</information>
<security>
<all-permissions/>
</security>
<resources>
<j2se version="1.6+" href="http://java.sun.com/products/autodl/j2se" max-heap-size="128m" />
<jar href="jarname_V1.2.12.jar" main="true"/>
</resources>
<application-desc main-class="package.module.LauncherJws">
<argument>--id-user=123456789</argument>
</application-desc>
<update check="background"/>
</jnlp>

We tried to change the update check attribute value with timeout but result is the same.
We tracked http traffic and the attribute if-modified-since is not transmitted when jar is downloaded.
By launching jnlp with instruction -verbose, we found the following trace (only when jar is donwloaded)

network: cache entry not found [URL: http://server/common/installs/jws/jarname_V1.2.12.jar version: null]
network: Found cache entry [URL: http://server/common/installs/jws/jarname_V1.2.12.jar version: null]
basic: impossible to launch from cache. Attempt with the online mode. [Some of required resources are not cached.]

(traces are translated from a french log)

This track is not displayed when the module starts without downloading.


REPRODUCIBILITY :
This bug can be reproduced often.