Last Modification Date from Solr search is always displaying the latest major version date

Steps to reproduce:

1. Create a new page (P1) - note the date of v1.1
2. Search for P1 using Solr - note the date
3. Add a comment to P1 - v1.2 will be created with another date
4. Search again for P1 using Solr - note the date has NOT changed

Expected result: On step 4 the date should be the same as the one for P1 v1.2.

Actual result: Solr displays the date of P1 v1.1, the latest major version.