Negative mean coverage returned by dnmtools pmd #255

Hello, I'm running PMD calling for multiple cell types by

$ ct=c0
$ dnmtools pmd -b 1000 -o 1kb/${ct}.pmd.b1k.bed -p 1kb/${ct}.para.b1k.tsv -v -D input/${ct}.meth

It succeed in some cell types, but failed in others. When failed, the verbose always reports a negative mean coverage, like

[READING IN AT BIN SIZE 1000]
[READING CPGS AND METH PROPS] from input/c0.meth
TOTAL BINS: 2809085
MEAN COVERAGE: -305.393
EXITING: INSUFFICIENT DATA

If we check the input file coverage with awk, it looks like

$ awk '{sum1+=$6;sum2+=1}END{print sum1/sum2}' input/${ct}.meth
610.82

I'm using the conda installed dnmtools version 1.4.4. An example input file can be downloaded from here.

Your help is highly appreciated!