Reproduction steps:
1) Open attached project
2) Enter play mode
3) If "SpaceOccupied" value is not 0 then press "ClearCache" button;
4) Press "D1" button and wait for downloading of asset bundle to finish
--- After downloading script calls "AssetBundle.Unload(bool)" method
--- In "AssetBundles" section cached asset bundles are marked in yellow color
5) Press "D2" button and wait for downloading of asset bundle to finish
6) Press "D3" button and wait for downloading of asset bundle to finish
--- After this step cache is almost full and there is not enough space for another one asset bundle
7) Press "D4" button

ACTUAL RESULT:
When you press "D4" button the warning message appears in Unity Console: "Not enough space in cache to write file". The asset bundle is being downloaded but not cached.

EXPECTED RESULT:
New asset bundle should be downloaded and cached, while the oldest one should be removed from cache (they all are UNLOADED - AssetBundle.Unload(true) method is called on each of them).

Regression introduced in version 5.3.2p1