recent item - PDF

[Herr Oswald <herr_oswald gmx de>]

Hello,

new to this list, I'm not sure whether it's the right place; if not,
please direct me to the most suitable one.

I'm on GNOME 3.28.2 with ubuntu 18.04. 

When I create a odt document, it almost immediately appears in the
"recent items" list of nemo, or in the file picker of some other apps
(tried evolution and LibO). 
But a PDF, created from my odt doc, takes a very long time (hours,
maybe days) to make it into the "recent items" list. But finally I can
find PDFs there as well.
Is there any configuration I can try - or is it a bug?

Cheers,
Wolf