This bug occurs when using kwin as window manager (kubuntu flavor) and is
easily reproducible on either upgrades and new installs of Kubuntu Precise. It
doesn't occur with Unity or Gnome.

There are other ways to trigger the bug but the easiest way is the following.
1) In Evolution you need at least 2 e-mail accounts (mine are both of the imapx
type)
2) Create an empty new e-mail
3) Type some text in the body
4) In the From: field select another account
5) Try to continue typing in the body

At this point the keyboard doesn't respond. You can copy/paste text using the
mouse.

6) To work around: right-click in the body, select input method , switch to
None or Simple
7) You can now type again.

Other ways to reproduce:
In Ubuntu I found the gtk3-demo in package gtk-3-examples.

In the comboboxes example I find:
- I can't type in the Editable box at all
- In the String IDs box behavior is exactly as in Evolution: get's stuck when
switching one of the Stock icons/ Where are we? box,then  after switching input
method it works again.

I use oxygen-gtk and found that switching to QtCurve or Raleigh the problem goes away.

Ferry