It ultimately depends on how the start pointer and the function are written, but in general, with ATL pointers and functions coded as they should be:

In debug mode:

CComPtr<ISomeComObj> mycomobj;
SomeOtherComObject1->FunctionToFindComObject(&mycomobj);
SomeOtherComObject2->FunctionToFindComObject(&mycomobj); // will throw an ATL assert

Extract from atlcomcli.h:

...
//The assert on operator& usually indicates a bug.  If this is really
//what is needed, however, take the address of the p member explicitly.
T** operator&() throw()
{
    ATLASSERT(p==NULL);
    return &p;
}
...

In release, you'll have a problem. So what you should do is this:

CComPtr<ISomeComObj> mycomobj;
SomeOtherComObject1->FunctionToFindComObject(&mycomobj);
mycomobj.Release();
SomeOtherComObject2->FunctionToFindComObject(&mycomobj);

Note it's good to know CComPtr::Release() can be called safely (in debug and release mode) even if the contained pointer is null, so this works fine for example:

CComPtr<ISomeComObj> mycomobj;
mycomobj.Release();

PS: my advice is always use debug mode to develop.