Different results using PARFOR and FOR - matlab

Question

I'm sorry that currently I'm not able to boil my code down to a minimal example.
It's a huge bunch of image processing code.
I have a loop that iterates over images (descriptors in variable stphogs) and for each image runs a detection.
function hogpatches = extractDetectionsFromImages(stphogs, poselet)
hogpatches = cell(1,length(stphogs));
parfor i = 1:length(stphogs)
tmp = extractDetectionsFromImage(stphogs(i), poselet); %e.g. 1x6 struct
if ~isempty(tmp)
hogpatches{i} = tmp;
end
end
hogpatches = cell2mat(hogpatches);
end
So this is the main loop. But the function calls in extractDetectionsFromImage go very deep.
My problem: Running this with a normal for-loop gives the correct result. When using PARFOR as above, hogpatches only contains 5 instead of 18 structs.
Where can I start to look for the error? I had a global variable the program did change. I removed that already. There is still a global variable 'config' which is however only read.. Any other hints? What could be the problem?
EDIT:
Even if I just run one iteration (size of stphogs is 1), the parfor fails. It doesn't have anything to do with the isempty part. Problem persists if I remove that.
EDIT2:
Ok here I boiled it to a minimal working example.
It is indeed caused by a global variable:
function parGlobalTest()
global testVar;
testVar = 123;
parfor i = 1:1
fprintf('A Value: %d\n', testVar);
testFunction();
end
end
function testFunction()
global testVar;
fprintf('B Value: %d\n', testVar);
end
In this example. The output for A will be 123, for B it will be nothing (undefined).
Why is that?

Answer 1

Ok, here is my solution:
function syncTestVar()
global testVar;
save('syncvar.mat', 'testVar');
pctRunOnAll global testVar;
pctRunOnAll load('syncvar.mat');
end
If someone has a better approach please tell me... This one works though
Btw: The save/load is needed because in my real program, testVar is a complex struct