It's not possible to download this example, so I have no idea about Informatix's code.
But I did somehow an overflow window and there are reasons to expect that this window is created inside a service.
If so, it's not difficult to understand why keyboard is not shown. For Android is active an activity, which belongs to another app.
I see relatively simple workaround.
Overflow windows receive touch / click events. So it's possible to detect that a user clicked an EditText and to execute following actions:
1) create and start transparent activity with "new" EditText (the text from EditText inside overflow window)
2) hide temporary your overflow window.
When user willl finish input in activity:
1) show overflow window again
2) correct a text in "old" Editext
3) finish an activity.