Jira connector is not able to connect to repository throug firewall while Eclipse internal web browser does

[TPD]

I'm working as a consultant at a customers location and try to connect to my employers jira v6.0.8 repository on a customers Laptop which is running Windows 7 (64bit).

That connection works great when I use this Laptop at home, so its not an issue of my employers firewall.

When I'm at the customers network eclipses internal webbrowser is still able to connect to the jira URL but the (Atlassian) Mylyn Jira connector runs into a timeout.

The repository configuration is set to use the global eclipse proxy settings.
The Eclipse Proxy settings is configured to "native"
The Java control panel network configuration is set to use a proxy configurtion script.

The proxy uses active directory single sign-on authentication.

Did someone run into the same problem?
How can I track down the root cause?

bye
Thomas

my Eclipse version is:
Version: Kepler Service Release 2
Build id: 20140224-0627

Mylyn version(s):
org.eclipse.mylyn_feature (3.13.0.v20140826-1734) "Mylyn Tasks"
org.eclipse.mylyn.bugzilla_feature (3.13.0.v20140830-0030) "Mylyn Tasks"
org.eclipse.mylyn.builds (1.5.0.v20140830-1416) "Mylyn Builds"
org.eclipse.mylyn.commons (3.13.0.v20140704-2323) "Mylyn Commons"
org.eclipse.mylyn.commons.identity (1.5.0.v20140702-2248) "Mylyn Commons"
org.eclipse.mylyn.commons.notifications (1.5.0.v20140702-2248) "Mylyn Commons"
org.eclipse.mylyn.commons.repositories (1.5.0.v20140905-0008) "Mylyn Commons"
org.eclipse.mylyn.commons.repositories.http (1.5.0.v20140702-2248) "Mylyn Commons"
org.eclipse.mylyn.context_feature (3.13.0.v20140819-2236) "Mylyn Context"
org.eclipse.mylyn.discovery (3.13.0.v20140820-1854) "Mylyn Commons"
org.eclipse.mylyn.hudson (1.5.0.v20140702-2228) "Mylyn Builds"
org.eclipse.mylyn.ide_feature (3.13.0.v20140702-2225) "Mylyn Context"
org.eclipse.mylyn.java_feature (3.13.0.v20140819-2236) "Mylyn Context"
org.eclipse.mylyn.monitor (3.13.0.v20140702-2155) "Mylyn Commons"
org.eclipse.mylyn.tasks.ide (3.13.0.v20140704-0050) "Mylyn Tasks"
org.eclipse.mylyn.team_feature (3.13.0.v20140702-2225) "Mylyn Context"
org.eclipse.mylyn.versions (1.5.0.v20140702-2223) "Mylyn Versions"
org.eclipse.mylyn.wikitext_feature (1.8.2.v20140211-0100) "Mylyn WikiText"

Atlassian connector version:
com.atlassian.connector.eclipse.jira (3.2.2.v20130909) "Atlassian Connector for Eclipse Branding"
com.atlassian.connector.eclipse.monitor (3.2.2.v20130909) "Atlassian Connector for Eclipse Branding"

[TPD]

Meanwhile I found out that the connector works well, when I either enter proxy data directly in the Jira-Repository configuration or change Eclipses proxy configuration from "native" to "manual". How ever, not using the Java-Controls proxy configuration forces me to enter a password in the respective configuration page and keeping that in sync when I have to change it (every couple of weeks). bye Thomas