Some Apps won't back up to iTunes

[inscrewtable]

When I back up or sync my iPod Touch to iTunes on my Mac, all the apps I have downloaded are transferred over and this has been consistent. However suddenly the last few apps I have download show up on the screen previews in iTunes, but they will now transfer over so they do not show up in the list of apps with either a 'remove' or 'install' button next to them. The only thing I have done different is that I'm running ios9 and iTunes 12.3.

Is there something really obvious that I am missing here?

 

[inscrewtable]

OK, I just got an answer back from Apple. Apparently ios9 does not tranfer apps over to iTunes any more because only the specific components of an app that are relevant to the device it was downloaded to are downloaded. So if you want new apps backed up to iTunes you have to download them to iTunes from the App store which downloads the full App. So the 'Transfer Purchases' menu option in iTunes is sort of redundant.