I'm riffing off an impassioned post by Matt Houlbrook on the exploitation of historians and the invisibilisation of their labours by, for example, the media (as well as unattributed citation in the blogosphere). And like him, I could rant for a considerable time about 'media researchers' (and as an archivist I possibly encounter even more of these) who expect what is often a substantial amount of free labour which may not even come to anything ('we're thinking of developing a programme...').
But what this made me think about was the failure to give due credit even within our actual profession, by senior figures in the field who should know better. This is a rather different matter from the people who write novels or plays based on an incident or theme in history that they have discovered in some historical monograph, though one does feel that acknowledgements to source are due in an afterword, if not a preface.
Some years ago I went above and beyond any responsibility I might have as archivist looking after a particular collection of papers, by identifying for a well-known historian, who had only a short time to pursue research into what is a very extensive collection of correspondence, not thematically organised, a selection of letters within it dealing with a particular topic, as I had published on this myself and was able to retrieve the information from my notes. When the work of which this formed an admittedly minor part was published, there was no citation to my work, a very strong implication that the author had found this collection all on their own, and interpretations applied which I felt possibly unjustified by spending a few hours consulting what was, after all, a small if hopefully representative selection. This was, looking at other references, not the only place where the existing historiography of the subject was glossed over; the impression the work in question gave was that the author had made startling new findings - which anyone who knew the literature of the subject would have known were already well-established.
Books by well-known names, published by trade presses, tend to get reviewed in the general press, not merely the scholarly journals, usually (in my experience) by people who lack any background in the field and thus take as revelation matters which are hardly new to the historian.
I could think of other instances of lack of collegiality in failure to acknowledge assistance given, or indeed to make due attribution to precursors in the field. I don't think this kind of bad behaviour is universal, in fact it is sufficiently contrary to usual good practice that it is perhaps the more shocking when it occurs, but I wonder if the media-isation (as it were) of history puts pressure on historians (or their publishers) to claim that their work is sui generis and a wholly new revelation about some historical matter, rather than part of the ongoing collective process that history actually is.