Address of 'this' pointer in Inheritance hierarchy

I was debugging some legacy code and while doing that found some inconsistency in the address of this pointer in the class hierarchy like this:

#include <cstdio>
#include <vector>

class ROOT1 {
   public:
    ROOT1() {}
    void printsomething() { printf("ROOT1::printsomething %p\n", this); }
    virtual ~ROOT1() {}
};

class SUBROOT : public ROOT1 {
   public:
    SUBROOT() {}
    void printsomething() { printf("SUBROOT::printsomething %p\n", this); }
    virtual ~SUBROOT() {}
};

class ROOT2 {
   public:
    ROOT2() {}
    virtual ~ROOT2() {}
    void printsomething() { printf("ROOT2::printsomething %p\n", this); }
};

class CHILD : public ROOT2, public SUBROOT {
   public:
    CHILD() {}
    virtual ~CHILD() {}
    void printsomething() { printf("CHILD::printsomething %p\n", this); }
};
class GRANDCHILD : public CHILD {
   public:
    GRANDCHILD() {}
    virtual ~GRANDCHILD() {}
    void printsomething() { printf("GRANDCHILD::printsomething %p\n", this); }
};

int main() {
    try {
        GRANDCHILD* line = new GRANDCHILD;
        ROOT1* root1 = static_cast<ROOT1*>(line);
        SUBROOT* subroot = static_cast<SUBROOT*>(line);
        CHILD* child = static_cast<CHILD*>(line);
        ROOT2* root2 = static_cast<ROOT2*>(line);

        root2->printsomething();
        root1->printsomething();
        subroot->printsomething();
        child->printsomething();
        line->printsomething();

    } catch (const char* s) {
        printf("Throw %s, %d\n", s, sizeof(std::vector<void*>));
    }
}

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The output I am getting is:

ROOT2::printsomething 0x23cf2b0
ROOT1::printsomething 0x23cf2b8
SUBROOT::printsomething 0x23cf2b8
CHILD::printsomething 0x23cf2b0
GRANDCHILD::printsomething 0x23cf2b0

There is a difference between the addresses of 'this' pointer. If I just swap the order of inheritance, the addresses changes along the class hierarchy. i.e.

class CHILD :  public SUBROOT, public ROOT2

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Output:

ROOT2::printsomething 0xc9b2b8
ROOT1::printsomething 0xc9b2b0
SUBROOT::printsomething 0xc9b2b0
CHILD::printsomething 0xc9b2b0
GRANDCHILD::printsomething 0xc9b2b0

What could be the reason?