I have found that when you rename a column name by changing the capitalization, an error is produced when you try to insert data into that column. I'm guessing MSSQL does not see the capitalization as being different and leaves it as is.

Kentico v5.0.3733
MSSQL2008

Steps to reproduce:
1. Create a test BizForm
2. On the Fields tab, create a new field called "name" and Save
3. On the Fields tab, using the Advanced mode edit the field to be "Name" and Save
4. On the Form tab, create a custom form and insert the field code

Name: $$input:Name$$

5. On the Data tab, try to insert data
6. An error is produced:

An error occurred when saving data: [DataConnection.ExecuteQuery]: Query: INSERT INTO custom_test ([FormInserted], [FormUpdated], [name], [question1] ) VALUES ( @FormInserted, @FormUpdated, @name, @question1); SELECT SCOPE_IDENTITY() AS [testID] : caused exception: Cannot insert the value NULL into column 'name', table 'IPAGlobalCMS.dbo.custom_test'; column does not allow nulls. INSERT fails. The statement has been terminated.

A workaround is to delete the field and then create a new one instead of renaming it.