Issue Summary

Converting tag field type column containing date values to date field type in Confluence databases results in blank values.

Steps to Reproduce

1) Create a CSV file with lot of repetitive dates. 
2) Import this CSV file to a new Confluence database.
3) The dates will be imported as tag field. This is because if there is a lot of repetitive or non unique data Confluence databases will import this as a tag field.
4) Now try to convert the column to date type. The column will show as blank. You can bring the data back by converting this back to tag field.(Screenshot_1.png, Screenshot_2.png, Screenshot_3.png). 

Expected Results

Confluence database column containing tag field type and dates in its content should be convertible to date type.

Actual Results

Converting tag field type column containing date values to date field type in Confluence databases results in blank values.

Workaround

Create the Confluence database structure with correct data types before importing the data in CSV format. After that copy paste the date values.