Way to reproduce a bug:

0. Build scene with two cubes in two different layers (let say: layer 1, and layer 2). Turn off all layers.
1. Turn on layer 2, and then turn on layer 1 (layer 2 still on - shift key)
2. Select cube on layer 1
3. Go to edit mode
4. Toggle all layers with ` hotkey
-- to this point is attached blend file
5. Toggle (off) all layers with ` hotkey
as you can see - edited cube disappears
6. Try exit from edit mode

tested in:
r35853
r34076 - official build from blender.org site (blender-2.56a-beta-windows32.zip)
blender 2.49b - different result, because
1) you can't turn off all layers by ` hotkey
2) when you turn off layer with currently edited object by (numerical hotkeys) theb you still can exit from "edit mode"

interesting is that in 2.5 we cannot turn off layer with edited object in edit mode by numerical hotkeys, but only by ` hotkey
and then we can't exit from "edit mode"

summary:
open attached "edit_mode.blend", then toggle all layers by ` hotkey, and try exit from "edit mode"


My graphics card is integrated with motherboard:
Intel(R) G41 Express Chipset 8.15.10.1892 2009-09-02
Intel GMA 4500

Operating system:
Windows 7 Pro OA HP (32 bit) Service Pack 1

Computer:
Compaq 500B Microtower
Pentium(R) Dual-Core CPU E5400 @ 2.70GHz
RAM: 4GB (available 2.97GB)

cheers
thank you all developers for your hard work