Using the 1.6.5-rc2- 2010-11-21 nightly build

I have a capped collection called "hits2" which is set with a size of 1GB (if it means anything, I'm running into the same thing with a different collection capped at 100MB). When using the mongo shell and running distinct() on a particular key of the documents, it works fine until the capped collection is full. Now, most of the time that this is executed, I get the following error message:

> db.hits2.distinct("userName")                      
Mon Nov 22 10:41:08 uncaught exception: distinct failed: {
	"errmsg" : "exception: assertion db/../bson/bsonelement.h:448",
	"code" : 0,
	"ok" : 0
}

I can sometimes get the distinct() command to return results and sometimes it will return a partial list before throwing the error mid-way through.