My first thought are:

Please define what you mean when you 'soft code' a variable. Please give an absolutely clear definition. Define this in general terms and then define again in the specific context of Perl. Two definitions required.

Secondly:

Define sandbox program. What is this?

If necessary use a footnote section at the bottom of your question.

I don't know the answer to your question. However I have a feeling that your problem might relate to multithreading and associated problems. If I am at all right in this 'feeling' (i.e. I don't know): Then you might need to tell us what processor chip your using.