filter bam datasets on a variety of attributes (with tag)

I have a question (or maybe a bug) to report.
I am using the “filter bam datasets on a variety of attributes” at use galaxy.org
For bowtie2 generated bam files, Seems the XS: & AS: are not working properly.
I tried bam files generated with STAR, filtering by AS: is working as expected with eye inspection.
I am wondering whether the “filter” do not work properly with tags having negative values.
Thanks a lot if you can clarify on this.

Eg: filter a bowtie2-generated bam file with “AS:<-5” will give me a bam file with AS field all =0 (with eye inspection.)

@jennaj