Checkbox validation partially applies when browsing to previous user forms page

[ScopeyNZ]

Steps to reproduce

• Create a user-form required checkbox on a page that's not the first page
• View that userform and proceed to the page with the checkbox
• Before ticking the checkbox, browse to the previous page
• Browse forward again to the page with the checkbox
• Observe the label is highlighted to indicate an invalid state but the message explaining the state is not shown

Notes

I'm pretty sure this is to do with our custom validation JS in this module. This could be a problem with userforms though.