Steps to reproduce it:
1- Starup the portal
2- Download the solr web plugin from the MarketPlace
3- Shutdown the portal
4- Edit the file solr-spring.xml to configure properly solr
5- Startup the portal
6- Go to Control Panel/MarketPlace--> update Solr web plugin
Result: The file solr-spring.xml is overwritten and you lose your own configuration for solr.
Fixing this issue
LPS-17442 would probably solve the problem.
IMPORTANT: This probably occurs for every portlet with its configuration modified