To reproduce:
1. Open attached project "CapsTest.zip".
2. Open and Play "Test" scene.
3. Press "Caps Lock" on key board, and check the result.

Expected result: Event.current.capsLock returns true if capslock is turned on (as described in documentation. https://docs.unity3d.com/ScriptReference/Event-capsLock.html)
Actual result: Event.current.capsLock returns true, only while Caps Lock key is pressed.

Reproducible: 5.5.4p2, 5.6.3f1, 2017.1.0p2, 2017.2.0b5, 2017.3.0a2

Workaround:
http://answers.unity3d.com/questions/164795/unable-to-trace-capslock-on-and-off.html