Decal with scalar parameter on it's emissive channel material breaks dynamic shadow on Oculus SDK.

So I've searched the whole net about Oculus and shadow problem and I couldn't find any result, it has been 3 days me trying to find the issue why my dynamic cascade shadow flicker when decal appears and I couldn't find it till a few mins ago, looks like connected a scaler parameter ( with 0 as value not sure yet with other value) to emissive channel on the decal material with deferred render breaks dynamic shadow and sometimes it causes flicker. Since I'm using UE4 4.21 I can't comment on the version or check if this bug fixed or not. but at least I thought I should comment about it here in case anyone faces the same issue to save his time. this issue doesn't occur with SteamVR.