Currently how the settings file is retrieved (when both creating/deleting it and getting the actual settings from it) has limitations and will not work in certain edge cases, such as the following:
Single site installation using multiple subdomains (https://wordpress.org/support/topic/version-1-5-1-stopped-working-on-subdomains/). Before version 1.5 the advanced-cache.php drop-in was not delivering the cache for subdomains but the late cache delivery still did. Since version 1.5 the subdomains would not be delivered because the settings file can not be found (as it's currently looking at the request host) and there is now no longer a late cache delivery.
Single site without a proper primary domain redirect (e.g. both https://www.example.com and https://example.com return a 200 status delivering the same page). This would result in duplicate cached pages under each host, but the settings file should still be found to deliver the pages being cached. Cache delivery behavior is the same as above. Before version 1.5 the advanced-cache.php drop-in was only delivering the cache for the primary domain while the late cache delivery handled the other. Since version 1.5 only the primary domain would be delivered because the settings file could found while the it can not be found for the other.
Subdirectory network installed in a subdirectory itself and that subdirectory is included in the site address (e.g. https://www.example.com/wordpress/site). Before version 1.4 the settings file did not work for any multisite if not the main site. Since version 1.4 wordpress would always be chosen, leaving out the unique identifier for that site. There has not been any issues that have arose from this that I've seen so far, but it would be good to ensure it's supported by always getting the actual blog path even if there is more than one directory in the site address URL.
Currently how the settings file is retrieved (when both creating/deleting it and getting the actual settings from it) has limitations and will not work in certain edge cases, such as the following:
advanced-cache.phpdrop-in was not delivering the cache for subdomains but the late cache delivery still did. Since version 1.5 the subdomains would not be delivered because the settings file can not be found (as it's currently looking at the request host) and there is now no longer a late cache delivery.https://www.example.comandhttps://example.comreturn a200status delivering the same page). This would result in duplicate cached pages under each host, but the settings file should still be found to deliver the pages being cached. Cache delivery behavior is the same as above. Before version 1.5 theadvanced-cache.phpdrop-in was only delivering the cache for the primary domain while the late cache delivery handled the other. Since version 1.5 only the primary domain would be delivered because the settings file could found while the it can not be found for the other.https://www.example.com/wordpress/site). Before version 1.4 the settings file did not work for any multisite if not the main site. Since version 1.4wordpresswould always be chosen, leaving out the unique identifier for that site. There has not been any issues that have arose from this that I've seen so far, but it would be good to ensure it's supported by always getting the actual blog path even if there is more than one directory in the site address URL.