Intention behind this is actually Box inset being too tiny
to reasonably contain other insets like ERT.
http://www.mail-archive.com/lyx-devel@lists.lyx.org/msg188987.html
case TopButton:
case LeftButton:
case ButtonOnly:
+ if (hasFixedWidth()){
+ const int mindim=button_dim.x2-button_dim.x1;
+ if (mi.base.textwidth<mindim)
+ mi.base.textwidth=mindim;
+ }
dim = dimensionCollapsed(bv);
if (geometry(bv) == TopButton
|| geometry(bv) == LeftButton) {