I know i'm digging out the dead here but, since cauldron isn't compatible since it seems the plugin is "verifying" weather inventory is open or what ever, isn't it a feature easily disabled ? The trade works aswell, if you have inventory tweaks (forge mod) you can ctrl click to proceed, so its just a matter of not having the inventory close on you upon regular click. If you have any interest in helping me out, for free or not it'd be great, i've been around the entire web for months looking for an alternative, and there simple isn't one..... Cauldron devs are long gone... You're my only hope to have this cool feature on our server!! Thanks in advanced buddy, Running latest forge / kcauldron on ftb infinity 1.7.10mc.

I will not test and debug with cauldron, nor will I dig out and debug an old 1.7.10-version of Shopkeepers and try to retro-fit changes or bug fixes etc.
Simply removing that inventory verification check will probably clear the way for other issues that this check was meant to fix.

However, I give this one attempt, just in case this inventory verification check is really the only issue you have on cauldron. If this doesn't work for you for some reason I will not further debug or make further changes to this.

I took the v1.68 version of Shopkeepers (the last version that apparently supported 1.7.10) and simply removed the ui window validation check (4898aa1).
You can find the plugin here: www.blablubbabc.de/daten/Shopkeepers-no_ui_check.jar
This version is completely untested.

Thanks, again.

No problem. Glad this actually solved your issue.