[Flickr plugin] The number of pictures shown in the block doesn't correspond with the config

Steps to reproduce:

• As admin go to the site home and turn editing on.
• Add a Tags block to the page via the 'Add a block' link.
• Click on any tag in the Tags block. (If there are no tags available, add a tag to an item on the site or add a tag to the default collection via 'Manage tags' in the Site administration.)
• On the tag page, add the Flickr block via the 'Add a block' link.
• Edit the Flickr block configuration and fiddle with the number of pictures

Below is an explanatory screenshot showing different values and coresponding results