Admin loses admin rights after creating vendor?

-- HikaMarket version -- : 1.4.1

Hello,

Due to an unfortunate decision by previous people on the team, we have a HikaMarket 1.4.1 installation that apparently cannot be easily upgraded due to some client specific customization.

There seems to be an issue where when an Admin adds a Vendor, that Admin is immediately logged out and they are removed from the Administrator group. The Vendor is saved though.

I have read through recent release notes and some are vague, and I'm not sure if they apply to this particular issue. For example:

In 1.4.4: The ACL might not be re-saved correctly in some cases
In 1.5.1: Fixing some issues with the vendor+user registration, Fixing issues with mod_hikamarket module

"Fixing issues" does not tell us what exactly is fixed, so we're not sure whether it's worth applying the updates and then re-customizing, or if it'd be better to cherry pick some patches and apply to our customizations.

Could someone please:
a.) Confirm this is a known issue (user adding Vendor loses Admin rights) and
b.) What version specifically resolves this issue, if applicable?

In the meantime, our devs will now feel some pain due to performing customizations in a non-upgrade-safe manner....

Thank you.