Create the basic 3 items tree
 
item1
    subitem2
      subsubitem3
 
Join the item1 and subitem2. - And Subsubitem3 will disappear  
(if it does not (sometimes happens), repeat the trick with subsubsub4).
If you have a default folder containing all items (usually "Date Stamp"), you will see subsubitem3 there:
 
subsubitem3
item1 subitem2
 
Now save your file.eco (you'll see why).
 
Now apply any new filter, for example, apply a filter ToDo=today, or try to create a "Date Stamp" notepad, if it was not created earlier.
Ecco will HANG, taking exactly 50% of my cpu (it's core2 duo).
 
Bug checked with eccoext.exe 3.6.2.15, 4.0.0.1, and without eccoext at all.
 
Shut the hanged Ecco via task manager, open the saved file.eco again.
Now remove the subsubitem3 from the doc, and apply a filter again. It will work fine.