On my 

Pharo4.0
Latest update: #40609

Pressing Alt-Tab brings up a debugger. Debugging the method shows:

newPreviewMorph
"Answer a new preview holder."
self halt.
^ Morph new
color: Color transparent;
extent: self defaultPreviewExtent;
yourself.


On 16 May 2015, at 1:09 AM, Avdi Grimm <avdi@avdi.org> wrote:



On Fri, May 15, 2015 at 7:06 PM Carlo <snoobabk@gmail.com> wrote:
Removing the 'self halt' still works though.

Can you give me a little more detail about where to find this? Thanks!