Duplicate class attributes

I’ve inserted two Captchas into a CF7 from like this:

[f12_captcha f12_captcha-569 captcha:honey]
[f12_captcha f12_captcha-61 captcha:image]

The code created for an input field looks like this:

<input class=”f12c wpcf7-validates-as-required” data-method=honey id=f12_captcha-569 captchamethod=honey class=”wpcf7-form-control wpcf7-f12_captcha wpcf7-validates-as-captcha” aria-invalid=false placeholder=Captcha value type=text name=f12_captcha-569 style=”width:0; height:0; max-width:0; max-height:0; opacity:0;“>

As you can see, the HTML “class” attribute is used twice, which is an internal parse error and the second one will be ignored.

Am I doing something wrong, or is this a bug?

Thanks for the (otherwise) good plugin! Tim