IndexWriter.synced field accumulates data leading to a Memory Leak

I am running into a strange OutOfMemoryError. My small test application does
index and delete some few files. This is repeated for 60k times. Optimization
is run from every 2k times a file is indexed. Index size is 50KB. I did analyze
the HeapDumpFile and realized that IndexWriter.synced field occupied more than
half of the heap. That field is a private HashSet without a getter. Its task is
to hold files which have been synced already.

There are two calls to addAll and one call to add on synced but no remove or
clear throughout the lifecycle of the IndexWriter instance.

According to the Eclipse Memory Analyzer synced contains 32618 entries which
look like file names "_e065_1.del" or "_e067.cfs"

The index directory contains 10 files only.

I guess synced is holding obsolete data