This is a known bug. Since the file browser content is URL sensitive and the file browser is being opened when you are at the report-edit page the file browser is displaying .report files.
What you can do is just open the .report file from the backend on a notepad. From there you can change the path to any other path. Below is how the starting part of .reprot file looks like wherein you can make that change. Inside the file browser, you can right-click on .report file or .metadata file to find out their path and name on the server.
<reportName>Cross Tabular Report Conditional Formatting</reportName>
<location>1463377807724/1463377836985</location> **\\PATH OF THE METADATA FILE PROVIDE OR CHANGE HERE**
<metadataFileName>e9be6771-995b-40eb-a01c-304857a100a1.metadata</metadataFileName> **\\NAME OF THE METADATA FILE PROVIDE OR CHANGE HERE**
From Team Helical