In msgid "This will reset <b>all</b> shortcuts to their default values. Do you really want to do this?", <b></b> tag is not parsed and just displayed. Build Date & Platform: Build 2009-01-07 on Arch Linux
Nick recently committed something to xfce_message_dialog_show() which escapes markup text. <b></b> not being parsed is caused by that. I'll update the settings dialog as soon as possible.
Fixed in revision 29447: Remove <b> markup from the shortcut reset dialog text (bug #4785). I also updated all the translation files so that this string doesn't need to be translated again. Hope that with this, breaking string freeze is ... kinda ok :-/
*** Bug 4817 has been marked as a duplicate of this bug. ***