When a particular light cookie is assigned to a light, errors are thrown each time view is updated (clicking on Inspector items, panning and rotating, or when in play mode).

Steps to reproduce:
1) Open the attached project (cookieIssue.zip).
2) Play the 'Main' scene.

Errors are logged in the Console:
Assertion failed on expression: 'mainDirShadowLight != shadowMap.light'
Shadowmap already exists in the cache

Using Instruments on OSX shows that around 16GB of virtual memory is used (virtual memory is not shown in Activity Monitor FYI). IOKit is responsible for the leak. The editor becomes fully unresponsive after some time. The issue goes away when the cookie is removed from the directional light named 'CookieEverythingDirectionalLight'. The leak also occurs on iOS and OS terminates the app after a few seconds.

Reproduced on:
5.6.0a2, 5.5.0f1, 5.4.3f1, 5.3.7p1, 5.2.4f1