debugger versus primitive 19 "simulation guard"

Trying to debug step two times into...
     [  'a' ] newProcess
...hangs the image.

It works okay with...
Pharo5.0 update: #50495
NBCoInterpreter NativeBoost-CogPlugin-EstebanLorenzano.21 uuid:
4d9b9bdf-2dfa-4c0b-99eb-5b110dadc697 Apr  2 2015
By: Esteban Lorenzano <[hidden email]> Jenkins build #14904
Unix built on Apr  2 2015 00:51:53 Compiler: 4.6.3

but not with...
Pharo5.0 update: #50496
CoInterpreter VMMaker.oscog-eem.1630 uuid:
2ed025ea-f400-4440-8e8b-5aa46d06c9ab Jan 14 2016
21ec004cce7d26010c18d357c805a0e1a4ffe376 Date: 2016-01-14 11:42:33
+0100 By: Esteban Lorenzano <[hidden email]> Jenkins build #498
Unix built on Jan 14 2016 11:50:34 Compiler: 4.6.3


btw, the same case on Squeak-4.6-All-In-one and Squeak-5-All-In-One
both produce "Code simulation error."

Is it maybe related to... "another endless debugger loop"
https://pharo.fogbugz.com/default.asp?16877

cheers -ben