There are reply related settings in Tools > Options > Outgoing mail > Messages and replies.  Perhaps one of those is different in the one identity that is not behaving as expected

<p>In my reply options the first two boxes are checked: 1) Include the text of the original message in the reply; and, 2) Prefix text included from the original with">" markers. When I click on reply the original message is not there. Here is what I get:</p><p mce_keep="true"> </p><font size="2"><p align="LEFT">Date sent: Wed, 21 Aug 2013 11:21:26 -0400</p><p mce_keep="true"> </p><p align="LEFT">Subject: Re: Property for you</p><p mce_keep="true"> </p><p align="LEFT">From: LD</p><p mce_keep="true"> </p><p align="LEFT">To: "Robert H. Mulder" <the_real_agent_mulder@mindspring.com></p><p mce_keep="true"> </p><span lang="EN"><p mce_keep="true"> </p><p align="LEFT">> </p><p mce_keep="true"> </p><p align="LEFT">> </p><p mce_keep="true"> </p></span><p mce_keep="true"> </p><p mce_keep="true"> </p></font><p>The rest of the original message is missing. Any ideas what might be causing this?</p><p mce_keep="true"> </p><p>Bob</p><p mce_keep="true"> </p><p mce_keep="true"> </p><p mce_keep="true"> </p>

If the original message is HTML only then you need to also tick the 'For replies to HTML, preserve original's formatting' option.  Keep in mind that HTML messages with remote graphics will not show the remote graphics in the reply.  Also, I have encountered messages for which the original HTML content will not show up in a reply no matter which options are checked.  This is rare but is something to be aware of.  Attaching the original message to the reply is an option in these cases.

I have 4 other e-mail profiles and I am not encountering the same problem.  I had earlier ticked the "For replies to HTML, preserve original's formatting" but that did not make a difference.