I have seen a couple in my contract harvest runs. One was a homebuilt one and the farmer simply made a mistake, he was embarassed a little when it was pointed out to him just after it was finished. The other buggy belonged to two brothers who were large contract harvesters who ran several chaser bins and they decided to swap the unloading side on one so that it would be might be easier to unload into large trucks at the same time as other buggies. That was the idea anyhow, as the unloading tubes fold anyhow it never made much differance when unloading on the go. The buggies were made by Finch engineering