unexpected change in variable after python function call

Consider the following small python snippet where I add '2' to the first column of a 3 x 3 matrix:

import numpy as np

def changeValue(kernel):
    kernel[0,0]=kernel[0,0]+ 2 
    kernel[1,0]=kernel[1,0]+ 2 
    kernel[2,0]=kernel[2,0]+ 2 
    return kernel

myKernel = np.array((
 [0, -1, 0],
 [-1, 5, -1],
 [0, -1, 0]), dtype="int")
CVkernel=myKernel

print(CVkernel)
a=changeValue(myKernel)
print(a)
print(CVkernel)

I get the following output

[[ 0 -1  0]
 [-1  5 -1]
 [ 0 -1  0]]

[[ 2 -1  0]
 [ 1  5 -1]
 [ 2 -1  0]]

[[ 2 -1  0]
 [ 1  5 -1]
 [ 2 -1  0]]

The value of myKernel clobbers CVkernel. I think there is an unintentional call-by-reference (pass-by-reference?) going on but I am not sure why.

If I define the function slightly differently

def changeValue2(kernel):
    kernel=kernel + 2 
    return kernel

Then CVkernel is left untouched

[[ 0 -1  0]
 [-1  5 -1]
 [ 0 -1  0]]

[[2 1 2]
 [1 7 1]
 [2 1 2]]

[[ 0 -1  0]
 [-1  5 -1]
 [ 0 -1  0]]

What is going on here? I tried printing out the address register of the variables with print(id(kernel)) and print(id(CVkernel)) and that does not shed any light.

EDIT Even when I use a 'safe' function call, kernel=kernel + 2 , the id of myKernel and CVkernel are the same.

id of myKernel  139994865303344
myKernel 
[[ 0 -1  0]
 [-1  5 -1]
 [ 0 -1  0]]
id of CVKernel  139994865303344
CVKernel 
[[ 0 -1  0]
 [-1  5 -1]
 [ 0 -1  0]]

**call made to changeValue2**

id of myKernel  139994865303344
myKernel 
[[ 0 -1  0]
 [-1  5 -1]
 [ 0 -1  0]]
id of CVKernel  139994865303344
CVKernel 
[[ 0 -1  0]
 [-1  5 -1]
 [ 0 -1  0]]
output a 
[[2 1 2]
 [1 7 1]
 [2 1 2]]

Shouldn't the id of each variable be different if they are different instances?

Try it as below:

def changeValue2(kernel):
    kernel += 2 
    return kernel

It shows the result as below:

[[ 0 -1  0]
 [-1  5 -1]
 [ 0 -1  0]]
[[2 1 2]
 [1 7 1]
 [2 1 2]]
[[2 1 2]
 [1 7 1]
 [2 1 2]]

You know well that It's a call by reference, but, In case of kernel = kernel + 2, the left kernel becomes another instance. Simply, It is same as newKernel = kernel + 2.

So, I changed it to kernel += 2, and it modified original kernel instance.