Unable to publish HTML5 using DITA bookmap with fm components

I am unable to publish my DITA bookmap if the DITA topic files are saved as .fm. FM says: "An error occurred in the publish process. View the log file for more details" log file says: Unable to publish. "Validate XML source files and retry". It works if files are in xml format. Is the publish in HTML5 format is meant to work only with xml files?