I (and my customers) see the same problem. I have no solution.
Thank you so much for the suggestion, I've tried both Trusted-Only:true and Trusted-Library:true with no change in the behavior. We are not seeing mixed content dialogs.
Hoping that the next release of Java would improve this situation, I grabbed the EA for Java 7 update 40. However, EA for this release indicates that this problem just becomes more exacerbated. With the EA 40, my users will now have the same number of security dialog but will now be required to check a box for "I accept" and then click "run" 15 times. Total clicks to launch a fully signed, CA trusted application is now up to 30.
Can someone please help?
I have just found that the use of uppercase/lowercase has changed in 7U21.
We have been running with the codebase notation like this: codebase="http://SERVER:port/folder/file.jnlp" since Java 1.4.2
In 7U21 I get a dialog pr. jar.
If I change to: codebase="http://server:port/folder/file.jnlp " the dialogs are not shown.