When editing discovery rule GUI gives error:

"Discovery rule "tmpl1:zzz" already exists, inherited from another template."

for one of the linked template.

So you need 3 linked templates ("tmpl1" -> "tmpl2"; "tmpl2" -> "tmpl3") with discovery rule in "tmpl3". Steps to reproduce:
1. Go to "Configuration" -> "Templates".
2. Click "Create" and create template "tmpl1".
3. Click "Create" and create template "tmpl2".
4. Click "Create" and create template "tmpl3".
5. Click "Discovery (0)" in "tmpl3".
6. Create any rule.
7. Go back to "Configuration" -> "Templates".
8. Click "tmpl1" and link it to "tmpl2".
9. Click "tmpl2" and link it to "tmpl3".
10. Make sure you have it the same was as on attached screenshot "tmpl-discov-overview.png".
11. Click "Discovery (1)" in "tmpl3".
12. Click the name of discovery rule.
13. Click "Save".
14. Observe the error as on attached screenshot "tmpl-discov-error.png".

NB! The bug appears to happen when making steps 8 and 9. Mind that if you do them vise versa (first linkt "tmpl2" to "tmpl3" and after that "tmpl1" to "tmpl2") the bug won't happen. But even in this case any changes in "tmpl3" will not be propagated to "tmpl1".