Cannot import fonts into imovie

After switching to El Capitan, I have a problem with iMovie.

In a number of unfinished movies, I used a text font called "Glypha LT" , which I imported into font book myself. This used to be no problem, I could easily select the font under "show fonts" and use it in the titles as needed.

After the update, I had to add the "Glypha LT" font to font book again.

It does show up in iMovie. When adding a title page, I can change a text line to "Glypha LT". It shows correctly, while editing. As soon as I finish editing and close the title page, the font changes back to Helvetica.

I tried this with different title themes, but the result is always the same: It seems to work, while I edit the text, once finished the text is back to Helvetica.