HaplotypeCaller missing SNP calls

Hi

I am in the process of validating the HaplotypeCaller in gatk3.8, and it is missing some obvious SNPs in GRCh37.

Playing around with various parameters I can make the variant being called or not. Most intriguing using the HaplotypeCaller with standard parameters but only change the region to be called from 22:50502363-50502727 to 22:50502413-50502727 two of the missing SNPs suddenly appears in the vcf file. Please see the two scenarios below I have included the bed regions in the screenshot:

Thanks

Kim