Discrepancy between daily report or any other timeframe

Hi guys,
i've a discrepancy between statistics in daily reports or the download statisics for any other timeframe.

If I download a PDF document from my website the request shows in the Piwik Visitor Log.

The Download shows also in a search in the Download section. But only on the same day.
If the Date Range is set to Week, Month or any other Timeframe the Download is missing.



Stats:
Piwik 1.12
601973 visits, 348168 unique visitors
1356095 pageviews, 1022271 unique pageviews
47217 downloads, 40480 unique downloads
393786 outlinks, 326272 unique outlinks

General Settings:
Piwik archiving to trigger from the browser DISABLED
Process reports for today set to: 3600 seconds

Autoarchiving is setup with a scheduled task, executed every hour.
Is this a known Problem?

Thanks! Hannes