Steps to reproduce:

1. Create Template_A
2. Create Item_X(key:test) at Template_A
3. Create Template_B
4. Create Item_X(key:test) at Template_B
5. Create Template_C
6. Template_C link new templates Template_A and Template_B
7. Check item of Template_C

Result:

Existing items with same item key at Template_C.

Expected:

Error occuer when click Update bottan, if Template_C link new templates Template_A and Template_B.