Steps to reproduce:
Create a space with initial version in Source (Duplicate Pagetitles feature is activated)
Create a new page in initial version with page title "Page A"
Edit the page, change the page title to "Page A Plus" (permalink remains as "Page A"
Create a new space in Target
Publish the space to existing space in Target
Go to the published space in Target
A page has a page title "Page A Plus"
A page has a page title "Page A"
The issue is not reproducible with Scroll Versions and Remote Endpoint 3.2.3 on Confluence 5.9 and 5.10.
If Target has Scroll Versions installed, you can use this workaround.
After step #4 open the created space → Space Tools → Space Add-ons
Go to Advanced Settings → click on Manage Settings → enabled Duplicate Pagetitles → click Save
Click on Manage Settings again → disabled Duplicate Pagetitles → click Save
Publish to this existing space
De-activate duplicate pagetitle handling in authoring space
Confluence 5.9.10 — Source
Confluence 5.10.8 — Target
Confluence 6.1 — Source
Confluence 6.0.6 — Target