Splitter problem.

One of my editors uses popup window to modify some of properties.
Sometimes mouse down event pass through popup window and stops on the splitter on property grid, so i can resize it's columns.

I placed working example in attachment.

Thanks for reporting this.  This should only be an issue if the user resizes the grid columns after dropping down the popup.  Usually a popup would close when it loses focus so this would not be an issue -- this is so that the user can work with other controls that would otherwise be covered up by the popup.  I'd therefore suggest you either have the popup close when the user clicks away, or use an Expander rather than a popup (so that the grid cell expands to make room for the larger editor, rather than sitting on top of the other cells).

If you do want to keep the current behaviour of having the popup overlay the other cells and remain open until dismissed, then you can prevent resizing by adding the following Opened and Closed event handlers:

<Popup Opened="Popup1_Opened" Closed="Popup1_Closed">

private void Popup1_Opened(object sender, System.EventArgs e)
{
  TreeListView.SetAllowColumnResizing(Grid, false);
}

private void Popup1_Closed(object sender, System.EventArgs e)
{
  TreeListView.SetAllowColumnResizing(Grid, true);
}

You will need a recent nightly build to use the AllowColumnResizing property (it was added after RTM).  You can download the trial edition of the nightly build from here or the retail edition from the store.

Here is another example. It looks like resize works on PreviewMouseDown event, ignoring lost focus or anything like this.

This issue occurs because your popup does not always close when the user clicks away from it (you are relying on the LostFocus event rather than StaysOpen, and LostFocus does not fire unless a control within the popup has gained focus first).  I'd suggest you apply the changes I described previously in this thread (http://www.mindscape.co.nz/forums/Post.aspx?ThreadID=2441&PostID=7156); in fact, it's probably worth applying these regardless of how you handle closing the popup, since resizing is unlikely to make sense while the popup is open.