This has also been a known issue for me as well. I found it when I was trying to add validation expressions to those properties.
You can go into the db and locate the table dbo.ProfilePropertyDefinition. Change DataType on twitter and facebook to be the same as myspace,flickr, and linkedin. Ex. my datatype is 365.
For ProfilePicture, my DataType is 367, but this may be different from one install to the other.
No guarantees, so I'd backup my site first
