This bug was initially filed as https://javafx-jira.kenai.com/browse/JEM-193, however it looks like a problem in deploy code.
The problem is how applet jars are handled, if they are specified with whitespaces in the original web page. For example:
<applet ... archive="jar1.jar, jar2.jar">
Note the whitespace between ',' and 'j' chars. When such an applet is launched, Java Plugin notifies Java Usage Tracker, which results in the following record:
plugin2|<date>|<host>|http://web.page.url: launchjnlp= code=... codebase=... width=100 archive=jar1.jar, jar2.jar height=100| ...
It leads to jar2.jar being handled as a separate applet attribute, not as a part of "archive".
This problem was supposed to be fixed by JUT fix JDK-8030103, which introduced quote and innerquote chars support to JUT. Unfortunately, the bug is still there, which makes me believe it's a problem in a way how Java Plugin passes applet params to Java Usage Tracker.