Reproduction steps:
1. Open project in "MyRepro.zip" and open Scene "sdsd.unity"
2. HDRenderPipelineAsset Lit Shader Mode is Forward Only (Assets -> Settings)
3. There are 2 Cameras in the Scene: the Main Camera and an RTCamera which renders to Texture
4. Make sure that the Scene view window is either off or invisible
5. Enter Play Mode and toggle Area Light

Expected result: Light is disabled in both Main Camera and RTCamera
Actual result: Light is disabled only in one Camera

Reproducible with: HDRP 6.7.1 (2019.2.0b1), HDRP 6.9.2 (2019.2.17f1), HDRP 7.1.7 (2019.3.0f4, 2020.1.0a18)
Not reproducible with: HDRP 4.10.0 (2018.4.15f1), HDRP 6.5.3 (2019.2.0b1)

Notes:
1. If Scene view is left open the Camera that will fail to disable the Light might be the one in the Scene view
2. It seems that one Camera must render to Texture to reproduce this issue (no need to display it with a Material though)
3. I was not able to reproduce the bug using other than Area Type of Lights
4. In 2019.2 + (HDRP 6.7.1; HDRP 6.9.2) heavy glitching is involved
5. This is a package regression (regressed in 6.7.1)