Reproduction steps:
1. Open the attached project "case_1307386-ArrayInspectorBug.zip"
2. In the Scripts folder, click on "New Foo"
3. In the Inspector window change any element in the Values array, so it becomes an unsorted array
4. Click the Apply button and notice how the array is now sorted
5. Change any element in the Values array, so it becomes an unsorted array
6. Right-click on that element and choose "Duplicate Array Element"

Alternatively:
1. Add [NonReorderable] above public "int[] values = {};" in "Foo.cs"
2. Select the "New Foo" asset again
3. In its Inspector right click any of the arrays -> "Duplicate Array Element"
4. Observe that the Apply/Revert buttons are disabled

Expected result: Apply and Revert buttons are not disabled, and the array is not yet saved
Actual result: Apply and Revert buttons are disabled, the array is saved without Apply() method ever being called and the array is not sorted

Reproducible with: 2021.1.0b8, 2021.2.0a5
Couldn't test with: 2018.4.33f1 (failed to downgrade to a functioning project), 2019.4.23f1, 2020.3.2f1 (because of another issue, clicking on Duplicate or Delete options when right-clicking, does nothing), 2021.1.0b9 - 2021.1.1f1, 2021.2.0a6 - 2021.2.0a10 (because Apply and Revert buttons don't get enable when you change any element)