Title attribute of in FeedItem is replaced by null

I posted several FeedItems using Salesforce Rest API but the title attribute of <a> tags in rich texts were not working correctly for me.

For instance,

POST /sobjects/FeedItem/

{
    "ParentId": "5000o0000xxxxxxxxx",
    "Body": "<ol>\n    <li>\n        <a title=\"Google\" href=\"https:\/\/www.google.com\">Google<\/a>\n    <\/li>\n<\/ol>",
    "IsRichText": true
}

<ol>
    <li>
        <a title="Google" href="https://www.google.com">Google</a>
    </li>
</ol>

...would be parsed into

<ol>
    <li>
        <span dir="ltr" class="uiOutputText"></span>
        <a href="https://www.google.com" title="null" target="_blank"><span dir="ltr" class="uiOutputText">Google</span></a>
        <span dir="ltr" class="uiOutputText"></span>
    </li>
</ol>

...and displayed like

Any idea what's going wrong? Thanks.