Reproduction steps:
1. Open the attached project ("DELETEUnity55.zip") in Unity
2. Open the scene Gizmos
3. Make sure that the TopCamera gameObject is enabled
4. Observe that you can't see the light's gizmo in game view

Expected: The gizmo appears in all cameras that are directed to it.
Actual: The gizmo is only drawn for the camera with the highest depth

Also I attached a project for 4.7, where everything works
https://fogbugz.unity3d.com/default.asp?ixAttachment=152077&pg=pgDownload&pgType=pgFile&sFilename=834070+4.7+repro.rar

Doesn't work with: 5.5.0b3. 5.5.0b4, 5.4.1p1
Works with: 4.7.2f1, 5.0.4f1, 5.1.f1, 5.2.4f1, 5.3.6p5