Steps to reproduce:

1) Download attached project "New Unity Project" and open in Unity.
2) Open scene "Test" and press play.
3) Press left Alt and check Console tab. Its empty.
4) Press left Ctrl+Alt. In console tab is written "LEFT ALT".
Note:

Expected result:
It should be written "LEFT ALT" in Console tab without Ctrl button.

Actual result:
Without Ctrl button there is no written "LEFT ALT" in Console tab.

Reproduced with: 5.4.b20, 5.4.b21.

Not reproduced with : 5.2.4f1, 5.3.5p4, 5.4.0b19.