Go to Settings > Tags and labels, then try this:

1. Select one enabled tag: the "Disable tags" button is clickable, as expected
2. Select two enabled tags: the "Disable tags" button is clickable, as expected
3. Select one disabled tag: the "Enable tags" button is clickable, as expected
4. Select two disabled tags: the "Enable tags" button is not clickable
5. Select one enabled and one disabled tags: both "Enable tags" and "Disable tags" buttons are clickable, as expected

Case 4 looks like a bug: when two disabled tags have been selected, I should be able to enable both of them at once.