Heisenbug involving Destructors & GC - Help Needed

[Maxime Chevalier-Boisvert via Digitalmars-d]

I seem to have run into a heisenbug involving destructors and the 
GC. I'm kind of stuck at this point and need help tracking down 
the issue.

I put the broken code in a branch called heisenbug on github:
https://github.com/higgsjs/Higgs/tree/heisenbug

The problem manifests itself on runs of `make test` (my 
unittests), but only some of the time. I wrote a script to run 
`make test` repeatedly to try and find a solution:
https://github.com/higgsjs/Higgs/blob/heisenbug/source/repeatmaketest.py

The problem usually manifests itself after 5 to 15 runs on my 
machine. I get a segmentation fault, not always in the same 
place. The randomness seems to stem from address space 
randomization.

It seems the issue is caused by my freeing/reinitializing the VM 
during unit tests. More specifically, commenting out this line 
makes the problem go away:
https://github.com/higgsjs/Higgs/blob/heisenbug/source/runtime/vm.d#L741

Higgs can run all of my benchmarks without ever failing, but 
restarting the VM during `make test` seems to be causing this 
problem to happen. It's not impossible that there could be 
another underlying issue, such as the JITted code I generate 
corrupting some memory location, but it would seem that if this 
were the case, the issue would likely show up outside of unit 
tests. Any help would be appreciated.