[ Forte for Java, CE v. 3.0 (Build 010710_1)
  on JDK 1.4.0-beta_refresh-b70 ]

1. I've started clean IDE build
2. Opened 2 forms (e.g. "Ted" and "Finder" from
"yourUserDir\sampledir\examples\texteditor\Ted") - by doubleClick on
them
3. Switched to MDI through "Main Window menu bar" - "Tools" -> "Setup
Wizard" -> chose "MDI (Single Window Interface)" radiobutton
4. click to "Source Editor"

-> focus is lost in whole MDI - I can switch between components,
but can't e.g. write to Source Editor (!!!)
or can't rename some e.g. file by doubleClick (with bigger pause between
clicks) in Explorer, ...

Focus will be gained after switching from "GUI Editing" workspace to
e.g. "Browsing" and back - now you will be able to write to "Source
Editor" but after restart of the IDE is focus lost again ...