That's nice, but like your windmills panorama, it needs levelling. I don't know which stitcher you prefer to use, but it only takes about 40 seconds to do it accurately in PTGui using vertical line control points (http://www.johnhpanos.com/levtut.htm). Autopano Pro has a similar facility.
You are right.
In fact I have been carefull about the horizontal line, but worked too fast and did not verify vertical lines.
And again, you are right, it is so easy to do with autopano tool box.
Shame on me.
I will write a small note next to my computer to remember checking this for future panoramas.
Thank you for your feedback.