Steps to reproduce:
1) Create template "test" and link existing "Template Module ICMP ping" to it.
2) Assign "test" template to host.
3) Go to "test" template and disable item which actually belongs to linked template.
It would be nice for ability to disable linked template items through parent template if there is existing hosts already assigned to template.
Some good news: it is possible to disable linked template item through parent template if there is no hosts assigned to template.