Yep,
That's by design. According to the List Style (View/List Style) the thumbnail text is :
1/ Taken from the default field 'Name' when in 'Thumnails' List Style
2/ Taken from the default field 'Album' when in 'Album Thumbnails" List Style.
If you use custom fields for naming your albums and picture they wont display. But you can alway use the command 'Tools/Library Tools/Move-Copy Field' to Copy (duplicate) the content of your custom album and name fields to the default Name & Album fields. I know you will have duplicate fields in your database but BTW why do you need to set up specific fields for Album & Name for photos ?
I do organize my Photo and Music using the same Name & Album fields but I created custom fields for properties specifics to images and/or music. (e.g. Caption, Label, Shot conditions etc..)
Christian