[MapProxy] Seed script "forgets" a few tiles ?

[Lars Lingner]

Hello MapProxy List,

At my MapProxy installation I'm renewing the caches every week.

Therefore I configured a time via file

iib_germany_sw:
  caches: [obb_sw]
  grids: [obb_e3857]
  coverages: [germany]
  levels:
    from: 4
    to: 16
refresh_before
     mtime: /path/to/seedtime.txt

After a successful run I was curios whether there are files older than
seedtime.txt
I found a few files (204) which in fact are older and they got not
rerendered. All the files are also within the specified level range.

Does anybody know a reason why the seed script would ignore some of the
files?

Best wishes,

Lars