Very good observation. Most often, this is absolutely appropriate. For example: Die Schule, der Schultisch; der Abend, das Abendessen. The first word is often used like an adjective in these compositions, 'die Riesenfreude' = a huge joy, but gender and article relate to the word's base, which is in most cases the last component. There might be exceptions I'm not aware of right now though.
There is (in my experience) very little difference in the pronunciation. Technically you should be able to hear the extra 's' in 'isst' (i.e you would stretch the 's' slightly), but the native speakers I talk to are prone to speaking quickly and it is almost impossible to hear the difference. Context is very important in these cases.