We have identified a major bug in ReduceReads -- GATK versions 2.0 and 2.1. The effect of the bug is that variant regions with more than 100 reads and fewer than 250 reads get downsampled to 0 reads.
This has now been fixed in the most recent release.
To check if you are using a buggy version, run the following:
samtools view -H $BAM
This will produce the following output:
@PG ID:GATK ReduceReads VN:XXX
If XXX is 2.0 or 2.1, any results obtained with your current version are suspect, and you will need to upgrade to the most recent version then rerun your processing.
Our most sincere apologies for the inconvenience.