og_subgroups_get_tree(TRUE) does not force a new tree to be created.

This becomes a problem with, for example, changing the parent of a group node. Upon save, if, "node_access_records" performs behaviour dependent on the node_tree, calls to "node_subgroups_get_tree(TRUE) dont cause a new tree to be built.
Eventually a new tree IS built, but not until after the node_access_records (which is strange because node_access_records the the absolutely LAST call on the update function.

This can be fixed by a simple modification to
includes/tree.inc/og_subgroups_get_tree($reset = FALSE)
{ //Currently the tree is NOT rebuilt IF:
$reset is True
AND
the static variable $tree already contains stuff

Clearly, the meaning of $reset, is that the tree is rebuilt regardless of whether it has been built already.
I have made a simple change to a single conditional to fix this:
//From if (!$tree)... to ...
if ($reset || !$tree) {
$tree = _og_subgroups_get_tree();

// Cache this tree in the database
cache_set($cache_key, $tree);
}
}

Ive included a patch

Ive made some modifications to OG to integrate better with potential og subgroups development, and am working on some powerful tools for OG_subgroups usage.

Hope I can be of help further and maybe contribute to this project more?