Unable to create thread reply via REST API with embedded emoticon

Hi,

I'm currently trying to create threads and thread replies via the REST API where the body could contain emoticons.  When emoticons do not exist in the body, they are correctly created, however, when they do, I am getting an error returned. For example, a POST to:

mycommunity/.../replies.json

with an sample body of;

Test Emoticon: <img src=\"/cfs-file/__key/system/emoji/1f609.svg\" />

Gets a response back of:

{
    "Info": [],
    "Warnings": [],
    "Errors": [
        "Only known URLs and the following file extensions are allowed: 123, aac, ai, aiff, art, asf, asx, avi, bmp, csd, db, dmg, doc, docx, drw, eml, flac, flv, gif, gz, ics, jpeg, jpg, log, m4a, m4p, m4v, mdb, mdbx, mid, midi, mmv, mov, mp3, mp4, mpeg, mpg, mpp, msg, ogg, ogv, pdf, png, pps, ppt, pptx, ps, psd, qt, ram, rar, rm, rtf, sit, sitx, sql, tif, tiff, txt, vcf, vcs, wav, webm, wma, wmv, wpd, wps, xls, xlsx, xml, zip. Please select a valid file or enter a valid URL."
    ]
}

I've checked to confirm that svg files are allowed, which they are so not sure what the problem could be/what I am doing wrong?

Has anyone seen this before or have a workaround for it?

This is for version 12.0.3.17950.

Thanks,

James.