I've been using Marketo Engage for almost 9 months, and I've seen this same issue with ANY superscript text - whether it's the R, TM, or even the ST or TH for dates (i.e. 29th, 21st). The space is added, and cannot be removed. HTML editing makes no difference, as it continues to appear in the sent version of the emails. Now that I'm thinking about it, there's also extra spaces added to hyperlinked text.
My "solution" has been to reword the content to not include the superscript to numbered dates, and to not superscript format any marks like (R), (TM), or (C). As for the hyperlinks... sometimes I get lucky and the spaces go away. Not sure how or why though.
If I add class="mktoText" to a <td> then Marketo editor adds a space wherever there's a beginning parenthesis. If I take mktoText out, no added spaces.
HTML Before mktoText:
The 2016 General Conference approved the celebration of United Methodist Volunteers in Mission Awareness Sunday (<a href="http://www.umcmission.org/volunteer" target="_blank">UMVIM Awareness Sunday</a>).
HTML after mktoText:
<br /> The 2016 General Conference approved the celebration of United Methodist Volunteers in Mission Awareness Sunday (
<a href="http://www.umcmission.org/volunteer" target="_blank">UMVIM Awareness Sunday</a>).
So it's like Nick mentioned. The editor is adding a trailing space on the new line that's added, but only in certain instances. Not sure what all those instances are, but it's annoying.
Marketo support got back and said:
The extra whitespace shows up before in certain cases because the email is split into separate lines before we send it out (to avoid problems with max line length problems https://tools.ietf.org/html/rfc2822#section-2.1.1). HTML then presents that linefeed as a space.
There is a workaround for this behavior. In the case of your example in the Community article, by surrounding the text with <span></span> you can force the entire element to be rendered as one continuous line. To do that, you need to click on the HTML button in the richtext editor and add <span> tags around the block of text that contains the <a>.
Another FYI. One of our admin thought they were doing the right thing by setting our "root block element" to div instead of p tags. They did it because they didn't like the email editor adding p tags which can cause spacing issues in some clients. However, using <div> tags as the root block element causes the aforementioned spacing issues. I switched it back to <p> tags and the spacing issues stopped. You can switch it here: Admin > Email > Edit Text Editor Settings > Email / Snippet Editor
Now that it's set back to p tags, if I add spaces in the editor (which I rarely do) I just change it from "double spacing" to "single spacing" to avoid p tags being inserted and potential spacing issues.
Adding a double space seems to default to a single space which has worked for me.
The code still sits on separate lines but removes any unwanted spacing.