Hi Dominic,
Nope, can't agree: this is MS 'fooling around'.
Check out the below link. That is an example of what a so-called 'floating crane' looks like, which are mostly used for handling bulk-cargoes:
http://www.ravestein.nl/images/enpont8.jpgThe crane in the screenshot above looks to me as a standard container bridge-crane (haven't seen any other ones yet in MSFS), which to the best of my knowledge are never mounted on pontoons/barges (except perhaps when they are being shipped from where they are constructed to the location where they are being put to work). Wouldn't make sence to erect them on a barge as it would just slow down the loading/discharging process of container ships (in this case).
Should know what i'm saying: am working in the maritime industry for the past 15 years, first as nautical officer onboard, and since a few years now in the headoffice of a large german shipowner...
Doesn't change anything to the fact though that the screenshots above are nice. Love the PMDG 747...
Cheerio,
Stef
EHM-1242