@fotoglut – Although we do have “third-party compatibility” code for Flattr in our plugin it should only be running if there is a “Flattr” class being found.
Specifically here:
../wp-content/plugins/nextgen-gallery/products/photocrati_nextgen/modules/third_party_compat/module.third_party_compat.php:399
We run this as a test:
if (!class_exists('Flattr'))
return;
Please double check to ensure you are not using a plugin or your current theme is calling this class.
Otherwise, if necessary (although not recommended due to it not being update safe) remove that specific section of our third-party compatibility code.
Thanks!
– Cais.