Reproduction steps:
1. Open the attached project ("case_1222305-Gamepad_Initial_Stick_Values.zip")
2. Open the repro scene ("SampleScene")
3. Enter Play Mode
4. Select the "Gamepad Info" object in the Hierarchy
5. Move controller's joystick and hold it in a stable position
6. Change Editor's focus by clicking on Console or Inspector windows
7. Inspect the joystick position output

Expected result: Joystick position remains the same
Actual result: Joystick position changes when changing window focus

Reproducible with: 2019.3.5f1, 2020.1.0b1, 2020.2.0a2
Couldn't test with 2017.4, 2018.4 (minimal required package version is not supported)
Reproducible with package versions: 1.0.0-preview.4, 1.0.0-preview.6
Not reproducible with package versions: 1.0.0-preview.3

Notes:
1. Changing the joystick value and returning to the same window resets the value to the old ("cached") value
2. Tested with Xbox controller