Can't export data / Dashboard rows to display undefined


I’m pretty new to Piwik.
I run two installations (on different servers for different reasons), both updated to 1.9.1
I’ve got no problems with the first one.

But I don’t get what’s wrong with the second:
Opening the standard Dashboard i always get an undefined “rows to display” in the “visits over time” widget. No matter the time period. (see screenshot)
When changing the input field to any other value - the widget just keeps loading forever.

And I can’t export any widget from dashboard to CSV or anything else, because idSite and period both are “undefined”:

But this works with the “Visitors - Overview”.

I have disabled the archive trigger, set up the cronjob …
I’ve set an higher php mem_limit and execution time, I get no http_log errors. RHEL6 / Apache 2.2.15 / PHP 5.4.8
Overall Piwik performance is very good.
Ah yes - I import logfiles into piwik, I don’t use the JS … but that shouldn’t be the problem?

update to this bug is now fixed