EDIT 1
To be more specific:
- I'm using "multiple file upload" to add files
- I'm letting Phocadownload create the file's "titles" from the file name (i.e. I don't set the titles individually)
- The file titles initially included the file extension
- I have (somehow) changed this behaviour, so that the titles no longer contain the file extension
Edit 2
Nevermind, I found it. I misremembered things, so I was looking for the wrong kind of settings. It is the setting "Show Filename or Title" in the "View" -> "Categories and Category View" options.

