[gtkmm] collapse_row(path) - strange problem

[Igor Gorbounov <igorbounov voronezh serw ru>]

When I try to do
path.up();
MyTree->collapse_row(path);
somewhere in the middle of a tree (as a reaction for a mouse click on a 
row)
- collapses all the tree. And even if I try to do
MyTree->expand_all() (or expand_to_path(path)) - nothing happens, all the
tree remains collapsed.
But if I repeat everything (not exiting application, just expanding rows by
hand and then clicking some row) - everything works Ok: all children of
a clicked row disppear and only this row becomes collapsed.
What's wrong with this tree?
   Hopefully,
       Igor Gorbounov