By validating the last element (instead of the first), it might be possible to remove the requirement to have custom error positioning code for checkable groups.
I would support this. Actually both elements should be validated, but the error should be always placed after last element for the group.
Here is the solution - http://stackoverflow.com/a/9219603/604388
Seems like this would be a better, more generic approach than my PR #400
The solution referenced on the SO question might be okay as a workaround, but we can do better when integrating directly in the plugin.
I'm sorry for the lack of activity on this issue. Instead of leaving it open any longer, I decided to close old issues without trying to address them, to longer give the false impression that it will get addressed eventually.
To the reporter (or anyone else interested in this issue): If you're affected by the same issue, consider opening a new issue, with a testpage that shows the issue. Even better, try to fix the issue yourself, and improve the project by sending a pull request. This may seem daunting at first, but you'll likely learn some useful skills that you can apply elsewhere as well. And you can help keep this project alive. We've documented how to do these things, too. A patch is worth a thousand issues!