[plt-scheme] .java sources and -composite.zo files

I've observed that .java sources at times can generate two .zo
files.

E.g., $PLT/collects/htdch/graphics/CommandSequence.java generates:

$PREFIX/lib/plt/collects/htdch/graphics/compiled/CommandSequence.zo

and, at times,

$PREFIX/lib/plt/collects/htdch/graphics/compiled/CommandSequence-composite.zo

What are these -composite.zo files and when do they get
generated?

I'm trying to track down a DrScheme packaging problem on
FreeBSD (4.11/6.1).  The DrScheme build process appears to
build these -composite.zo files intermittently in the
installation directory, making it hard to create a consistent
manifest file for the package.

Regards,
Koshy