Uh-oh: I relaunched my Xterm configuration and it now works. Sorry for wasting your time. (My friends actually misunderstood my question…)
Thanks, I checked with several friends on other machines and either Firefox or Chrome and they mentionned the same issue: ok on individual posts and not ok on main page Very curious.
Thanks: in the post itself, http://xianblog.wordpress.com/2012/11/19/amis-convergence-at-last/, the image is indeed completely correct.
When looking at the blog page, http://xianblog.wordpress.com, the same image gets larger.
Another illustration is http://xianblog.wordpress.com/2012/11/18/rue-de-grenelle-doors/, where the six pictures go two by two on the post, but get garbled for the last two images on the main page http://xianblog.wordpress.com
This is new, the older posts did not suffer from this disease…