When you look at the raw page (select the page and goto File -> Download) in an editor and look for this datum, are all the elements under the datum still there? You can also do this in the component itself with the component editor, clicking preview, then setting the Default content, saving, then look at the data section int he component editor. I had seen an issue where sometimes on save the update of the component data elements failed to rewrite all the elements under the Datum. The workaround was making sure the Exposed="false" was on each datum in the parameters element but it looks like you have that. Is it possible it's occuring on another instance of the datum and you don't have Exposed="false" ?
