Trashing the prefs didn’t help.
Neither did copying the sequence in to a new project.
But after I trashed the prefs one thing did happen: The modified size changed a little when I checked and unchecked “Include master clips outside the selection” – but not nearly enough.
see at https://nisboye.dk/FCP_2.jpg and https://nisboye.dk/FCP_3.jpg
132 GB seem a little to much for a 100 minutes of DV footage…