Dolphin doesn't show up-summed duration of multiple files

[Jonas Baumgardt]

Dear Sir and Madam,

I think I have discovered a bug in Dolphin, but I'm not completely sure.
If you select an audio- or video-file and if the information-bar is 
enabled, you can see the duration of the file. But when you select 
multiple files of the equal file format, it doesn't shows the up-summed 
duration of the selected files.
I once opened a ticket at the Manjaro-forum and some of the users 
answered, that they can sum up the duration of multiple files.

Is there a special option, which I have to enable or where is the problem?

I'd be glad to your from you soon.

Yours sincerely,
Jonas Baumgardt