Strange AggregatePlots with diagonal

[robertferr]

I am using an older version of hicexplorer to be able to use the function aggregate contacts with -genome option.

What I get is a nice aggregate plot, but in all of them there is a faint diagonal plotted. What is this?

command is:
hicAggregateContacts --matrix $1.h5 --BED $2.bed --outFileName $1_$2_genome_aggregate.png --numberOfBins 80 --avgType mean --vMin 0.0 --vMax 1.8 --range 500000:10000000 --transform obs/exp --genome

Thanks a lot