Created attachment 52061 [details]
example spreadsheet with described behavior (only reproducible with 3.4.3)

Problem description: 
When using a pivot table for aggregating data from mixed colums (text & numbers), the entries from the text column data should not be converted to numbers.

Steps to reproduce:
1. create a new spreadsheet
2. formate the first column as text
3. enter following data into a table

category  amount
01        3
02        4
01        2
03        7

4. create pivot table from the above table, draw "category" field into row fields, "amount" field into data fields.

5. Result: text entries "01", "02", "03" get convertet into (numbers) 1, 2, 3.

Expected behavior: 
Text should stay text, like in prior versions (e.g. 3.3.4)