Yes, with WoodWheels permission I have purchased it along with a couple other things from this Japan seller to take advantage of combined shipping (might as well!). The Listing covered everything, Tomy, Trackmaster, Plarail Thomas so can't tell from that. It does say Gullane 2011 Thomas Limited that might help one narrow it down so at least we know it came out within the last 6 years. Boy, I hope its not Capsule.
EDIT:
I think I may have found what set this came in, Thomas the Tank Engine Round and Round Bridge Set
http://www.1999.co.jp/eng/10146992 released in the middle of 2011. You can see the log wagon in the box pictures and in the description it states
"wobbling action freight cargo of logs" Interesting, can't wait to see how she works as it may look good having 4 or more being pulled around by a shunter. I am guessing that just the logs wobble as it uses an axle cam and not the whole wagon like the wobbly Troublesome trucks do with off set wheels. Mystery solved....right?
So it is a Tomy/Plarail wagon with buffers, they have made so many of this same wagons without...come on Tomy/Plarail how about making these and your tankers with buffers like this from now on....what you say?
EDIT#2:
And this video confirms that the logs undulate and not the wagon, pretty cool.