DefaultPlatform implementation ("the platform NB is running on") returns NB jars from its getStandardLibraries(). IMHO it should filter them out to provide view as similar as possible to a JavaPlatform for the same JDK instance set up explicitly in the IDE.
Fixed jet-main a9aa1802564e
Integrated into 'main-silver', will be available in build *201701290002* on http://bits.netbeans.org/dev/nightly/ (upload may still be in progress)
User: Tomas Zezula <email@example.com>
Log: #269510:Default platform reports NB jars as standard libraries