Merge duplicate contacts causes loss of Pledges

Pledges get lost if contacts are merged and the duplicate has pledges.

Reproducible on Joomla! version and Drupal demo r23950

Steps to reproduce.
1. Create a contact
2. Add a pledge
3. Create a second contact that will match the first on a dedupe rule (eg, same first name and last name)
4. Find duplicates using that rule
5. Select the pair for merging
6. Make the contact with the pledge the duplicate
7. Note that pledges are not listed as data to be preserved
8. Merge the contacts
9. Note that the merged contact has no pledges
10. Try and find the pledge via Find Pledges
11. Note the pledge is not listed (9 and 11 together suggest the pledge is deleted rather than detached from the contact)

PS: This affects 3.0.2, but that option wasn't supplied in the dropdown list