Add datetime property to "MetaInfo" field using SharePoint 2013 CSOM

When uploading a file along with metadata using SharePoint FP RPC (using the "method= put document") it allows me to properly add datetime properties. My metainfo looks like this:

Then later on, when I try to update "MyCustomDate" property from the "MetaInfo" field using CSOM, it fails while updating it. (In this case I am using CSOM because I am updating some more fields and I want to avoid extra round-trips)

After that update my metainfo looks like this: