Maybe someone should. But I haven’t seen it. Can’t confirm if it is a WP plugin. I assume that if many developers do have the same error, it is possible that the plugin is not well documented (if documented at all)
The site I first noticed it on was the Mazda UK site. There were also other problems on the same form:
Password: must contain upper or lower case letters - in fact after a couple attempts at setting a password I found it HAD to have both upper and lower case letters and nothing else.
Post code: normally I just input it in lower case letters and the code sorts it out. But again after two attempts I found it had to be exact - upper case letters and a space between the two parts.
On another site ( major UK bank ) I tried to send an email using the form and the first attempt told me I could not use certain characters; I can not remember what others were but one was | I was not using any of the illegal characters so I first removed the : but again the error. I then removed the ; but still had the error and in the end I had to take out every bit of the punctuation except the full stops!