How to reproduce:
1. Open new unity project
2. Open profiler window
3. Enter the play mode
4. Change items display type to a hierarchy
5. Select one of the items from profiler's hierarchy
6. Click again on the same item

Expected result: Item gets deselected
Actual result: Item stays selected

Reproducible with:2018.1.0a5, 2018.1.9f2, 2018.2.17f1, 2018.3.0b11, 2019.1.0a10
Not reproducible with: 2017.4.16f1, 2018.1.0a4

note: this makes reading timeline harder because it shows values of the selected item

Note: This fix does not add deselection on clicking the same item again, as that would be rather unique behavior within Unity. This fix allows for deselection if you click into a line of the hierarchy view that does not have any item in it.
Alternatively, and as another work around that worked before this fix already: you can also press Ctrl/Cmd + A to deselect.