Site template propagation executed multiple times in a single page load when layout friendly URLs are conflicting

• Type: Bug
• Status: Closed
• Resolution: Fixed
• Affects Version/s: 7.0.X, 7.1.X, 7.2.X, 7.3.X, Master
• Fix Version/s: 7.0.0 DXP FP97, 7.0.X, 7.1.10 DXP FP21, 7.1.X, 7.2.10 DXP FP10, 7.2.10.4 DXP SP4, 7.2.X, 7.3.10 DXP FP1, 7.3.10.1 DXP SP1, 7.3.6 CE GA7, 7.3.X, 7.4.13 DXP GA1, Master
• Component/s: Content Publishing > Site Templates
• Labels:
  • backend_test
  • ee-ts
  • liferay-dxp-72-sp4
  • liferay-dxp-73-sp1
  • liferay-fixpack-de-97-7010
  • liferay-fixpack-dxp-1-7310
  • liferay-fixpack-dxp-10-7210
  • liferay-fixpack-dxp-21-7110
• Branch Version/s:
  7.3.x, 7.2.x, 7.1.x, 7.0.x
• Backported to Branch:
  Committed
• Fix Priority: 3

Reproduction steps:

1. Start up the portal
2. Set the following log levels:
   com.liferay.portlet.sites.util DEBUG
   com.liferay.exportimport.internal.controller INFO
   com.liferay.layout.admin.web.internal.exportimport.data.handler.LayoutStagedModelDataHandler WARN
3. Create a site template
4. Create a site from this template
5. Add a new page to the site
6. Add a new page with the same name and friendly URL to the template
7. Refresh the site

Expected result: After one attempt, the site template propagation stops, and only restarts when the URL of the conflicting layout is actually changed.
Actual result: The site template propagation is started for every getLayout() call, even multiple times for one page load. This is visible from the many "Acquired lock..", "Applying layout set prototype...", "Released lock..." messages from the log. Also, the page load time is significantly longer than usual.

Notes:
There's a warning message visible in Configuration > Site Settings, on the Pages tab:

Some pages from the site template cannot be propagated because their friendly URLs conflict with the following pages. Modify the friendly URL of the pages to allow their propagation from the site template.