The small-figure macro does not indent properly the caption when placed inside a table (e.g. to place several figures side-by-side). The following redefinition seems to correct this problem:

<assign|small-figure|<macro|body|caption|<surround|<compound|next-figure>||<render-small-figure|figure|<compound|figure-text>
<compound|the-figure>|<arg|body>|<surround|<set-binding|<compound|the-figure>>||<arg|caption>>>>>>

the point is to add a \surround to the outmost environment. The problem has been reported on the forum here:

http://forum.texmacs.cn/t/what-is-the-recommended-way-to-insert-side-by-side-figures/852

Maybe other similar environments have the same problem.