Let me further clarify your confusion. Look at the following picture carefully (along with the color coding),
You can see that I've initialized the value of A in the first line in red color.
Notice that when there is a READ operation, then no change takes place either in the buffer or in the database.
When there is a WRITE operation, then changes take place at both the buffer and the database.
I've added an additional line A=A+5 (in green) so as to show you that here, changes will only take place in the buffer and not in the database.
Also the WRITE operation in the T2 will be a blind write just because it did not read the value of A before writing it in the database.