Just to separate the previous post.
There's an apparent conflict between Community Pack (CP) and Custom Fields (CF).
When both are loaded, a Custom date field can only be set to date and time. It cannot be set only to date or only to time.
Functionality of other CFs is being checked.
With MT42RC3, without a CP, there was no problem. The problem is with MTPro.
Reported on Movable Type 4.2
For an update see this post http://forums.movabletype.org/2008/08/community-pack-v-professional.html#comment-6537