What you have to know about vectors in c++ is that they have to use the copy operator of the class of your objects to be able to enter them into the vector. If you had memory allocation in these objects that was automatically deallocated when the destructor was called, that could explain your problems: your object was copied into the vector then destroyed.
If you have, in your object class, a pointer that points towards a buffer allocated, a copy of this object will point towards the same buffer (if you use the default copy operator). If the destructor deallocates the buffer, when the copy destructor will be called, the original buffer will be deallocated, therefore your data won’t be available anymore.
This problem doesn’t happen if you use pointers, because you control the life of your elements via new/destroy, and the vector functions only copy pointer towards your elements.