Google ignoring robots.txt file?

For varied reasons, I run a hybrid website - a lot of dynamic pages and a few static pages. Within the static pages, there are some iframes. The iframes point to a folder that contains some product images and descriptions, and some files that contain links to urls within the dynamic part of the site. In my robots.txt file, which was written in June this year, I have disallowed access to all bots to the folder that contains the iframes. I have run a "site:mysite/iframefolder" search and the robots.txt disallowed folders and the iframe urls are showing up. Has anyone an idea about why this has happened now and not before? I thought the search engines, and particularly Google ignored crawling/indexing pages that were listed in the robots.txt file? The robots.txt file was in place long before the iframe folders were uploaded. It isn't coincidence that a significant number of my product pages have now been seen as duplicate content and I appear to have been penalized. For clarity (afterthought) there are html links within the iframe pointing to areas of the dynamic pages. Am I right to assume that because the parent folder is disallowed, then the bots won't/shouldn't crawl the child files contained within that folder? Thanks in advance for any help on this