No saving of data after first run

[ThomasPWCope]

Dear Sir/Madam,

I am trying to test the simopt module. Having cloned it, and run the file "demo_problem_solver", I find it works as expected. However, after the first run, I find that no experiment data is saved. This persists if:

1. I change the name of a problem
2. I run the same problem and solver as the first run.
3. I delete all files in "experiments" and re-run.

Can you help me to understand what is going wrong?
Best,
Tom