vhpi start-of-restart callback

I'm running a vhpi C++ application. I'm having difficulty getting ncsim to call my start-of-restart function after a restart. Here's my sequence:

1) Start simulation A. I pass the -loadvhpi option to ncsim to load my C++ dlm.

2) Save a snapshot. My vhpi app saves a C++ start-of-restart callback function at this time.

3) Quit the simulation.

4) Start simulation B, again using -loadvhpi to load the same C++ dlm as in step 1.

5) Issue the Tcl "restart" command to restart the snapshot saved in step 2.

In step 5 I hoped ncsim would call the start-of-restart function I saved in step 2, but it doesn't always happen. For small, proof-of-concept simulations it works, but not for large simulations.