I think you may be misunderstanding, data is not being duplicated between the two tables. Let me try to explain again.
TableA:
Case_ID
Date
Customer Name
ShortDescription
LongDescription
Classification
TableB
Template_ID
TemplateName
ShortDescription
Classification
FormA is based on TableA. Totally straight forward so far.
On Form A is cmbTemplate which is populated with values from TableB.TemplateName.
The user starts a new blank form on FormA, Selects a value from cmbTemplate and clicks cmdTemplate. Based on what value was picked from the combo box, short description and classification populate with the appropriate values that were found in TableB.
That make more sense?