Okay, thanks for provided info. I found the source of the problem and fixed it.
@Jamie Please revise. Do you think it might cause issues with other modules comparing versions the new way?
Look, here is what we had, before the patch, when comparing minor versions, first containing underscore, against second that doesn’t have underscore, like 2.9.1-6.el7_2.3 vs 2.9.1-6.el7.4:
… and here is after the patch, which makes things right:
Note: In case you think it might cause issues with version compare in other modules, let me know, I will work around it, somehow.