To reproduce:
1. Create a new document. You can add content here or not.
2. Switch to Notes mode (either by clicking the Notes tab just above the slide,
or by View > Notes Page).
3. Add a note to slide one.
4. Switch to Normal mode (either by clicking the Normal tab just above the
slide, or by View > Normal).
5. Add a second slide (e.g. by clicking the Add Slide button on the tool bar, or
right clicking the left-side thumbnail of the current slide). You can again add
content or not.
6. Switch back to Notes mode.
7. Add a note to the second slide.
8. While the note is still in edit mode, click the thumbnail on the left for
slide 1.

Result:
The application crashes (see attached crash log).

Variations tested:
A. I tried the above with several different layouts, and with and without
entering data on the slides. It appears that having or not having data in the
slides doesn't effect this bug.

B. I tried creating both slides, then creating both notes, and then repeating
the final step above. This works correctly / no crash. It seems to crash only
when the steps include alternating between creating a slide and a note.

C. I tried my original steps above, but saving between creating the second note
and clicking the thumbnail. Impress still crashes.

D. I tried reopening the saved document created in C. above, getting back into
edit mode on the second note. Impress no longer crashes.