OSS v1.5.14 creates many temporary files

Hello
I am using OSS v1.5.14, and I have a problem : The webcrawler of OSS creates many files like oss*.pptx into /tmp/ folder. 
When I open a file, it's a file which has been crawled and indexed by OSS.

1/ Why the temporary folder is full of those files ? Is there any cause about this ? 
2/ how to automatically empty that folder ?

Regards, 