Critical bug in all versions of HoMM3
The bug occurs with and without HD.
Step-by-step instructions on how to trigger the crash:
1. Fill all 7 slots in the hero's army (e.g., with Azure Dragons).
2. Open the creature recruitment dialog (diplomacy or after using a skill, it doesn't matter). upd: There is no crash when recruiting through diplomacy. It seems the hero needs to be on the yellow tile of the object.
3. Remove one of the slots (it was 7, now it's 6).
4. Place the recruited monsters in the empty slot.
5. Without closing the recruitment dialog, open the hero's window by clicking on his portrait icon.
6. Click the left mouse button on, for example, a secondary skill. Then click OK to exit the description of the secondary skill.
7. Close the hero's window.
8. Close the recruitment dialog, and you'll get a crash at 0x4FD4A8.