How to reproduce : 

1 - On a french sitemap, on a page : 

• Add an attachment
• Display it by adding an attachment service to the (fr) page. 
• Add a search service configured with : 
  • Searched elements : "Documents"
  • Context :

2 - On the english sitemap, on a page : 

• Add an attachment
• Display it by adding an attachment service to the (en) page. 

3 - On french sitemap, perform search on the configured search service : 

=> Attachment to english page is returned whereas it should not.