Plugins in Custom Update Center appear as "Signed but not Trusted"

To be more specific, I am using NetBeans 8.02 still and the clients are using Java 8.0.74 that is bundled with the RCP app, built through Ant.

As an experiment I published another update through my update center. This time the Dialog stating all my nbms were signed but not trusted did not appear. I followed the NetBeans sourcecode and it appears that Java/NetBeans may treat all certificates as untrusted until they are accepted at least once by the end user.

If this is true, I still don't want my users to see this Dialog even the first time. It will confuse them and they may not trust my app. I paid for a code signing certificate so that all trust concerns should be minimized.

Any ideas how I can suppress this Dialog from appearing the first time?