Gthumb rename template not working

Hi all !

I wanted to rename my photos with the rename function of gthumb, but unfortunately the templates for the digitalization date is not fully working.
I want my photos to be renamed as follow : YYYYMMDD_hhmmss.jpg corresponding to the date when the picture was taken.
If I use the digitalization date ( %D) template, it will give me YYYY-MM-DD– which is not good.
But when I use the customized template %D{ %Y%m%d_%H%M%S } which should bo ok, it gives me the almost the same result : _YYYY-MM-DD–

I truely don’t understand, is there anything missing ? Do you have the same behaviour ?

Thanks for your help