Hi,
I believe I have found a bug where if you use the Link field and set it equal to a value it does not keep that value on a subsequent save. For instance, I have a link field and when I initially set it, it saves perfectly fine and I see the preview URL but it disappears if I save again.
Lets just say I need to access a content type and modify the value of another field. If I save again, the value that I had stored in the Link field is no longer present and gets deleted for some odd reason.