Code requirements for C++ plugin in Unity

I have some working C++ code that I would like to pull into Unity3d.

I am able to compile a bundle in Xcode and have it show up in Unity3d. Dummy functions within the plugin (e.g. a function I wrote called "ReturnFour", a basic function that returns 4) work fine. However, when I try to execute more complex functions, I get memory leaks:

 Here's the output from the crash report:
 
 Crashed Thread:        0  CrBrowserMain  Dispatch queue: com.apple.main-thread
 
 Exception Type:        EXC_CRASH (SIGABRT)
 Exception Codes:       0x0000000000000000, 0x0000000000000000
 Exception Note:        EXC_CORPSE_NOTIFY
 
 Application Specific Information:
 abort() called
 *** error for object 0x12ba79b20: pointer being freed was not allocated
  
 
 Thread 0 Crashed:: CrBrowserMain  Dispatch queue: com.apple.main-thread
 0   libsystem_kernel.dylib            0x00007fff84a2f002 __pthread_kill + 10
 1   libsystem_pthread.dylib           0x00007fff807ac5c5 pthread_kill + 90
 2   libsystem_c.dylib                 0x00007fff8bdca6e7 abort + 129
 3   libmono.0.dylib                   0x0000000109ca4e0e mono_handle_native_sigsegv + 732
 4   libmono.0.dylib                   0x0000000109cec8ff 0x109c32000 + 764159
 5   libsystem_platform.dylib          0x00007fff80c88eaa _sigtramp + 26
 6   ???                               0x000000012573ae41 0 + 4923305537
 7   libsystem_c.dylib                 0x00007fff8bdca6e7 abort + 129
 8   libsystem_malloc.dylib            0x00007fff89ffd070 free + 425
 9   libstdc++.6.dylib                 0x00007fff82c23d1c std::string::_M_mutate(unsigned long, unsigned long, unsigned long) + 332
 10  libstdc++.6.dylib                 0x00007fff82c247be std::string::assign(char const*, unsigned long) + 78
 11  com.yourcompany.ASimplePlugin     0x000000012594357c BioFVM::Microenvironment::Microenvironment() + 936 (BioFVM_microenvironment.cpp:91)
 12  com.yourcompany.ASimplePlugin     0x000000012592f0a7 PrintFour + 37 (trial.cpp:30)

I guess it's possible that my code has memory leaks, but It's been extensively tested in the past and I don't think it does.

Is there some basic memory requirement/compilation tag that I need to respect to produce a bundle that plays well with U3D?