Simple answer to the 8 + 8 = 10 is that 10 is the max we can have in the inventory at any one time so anyover and above that do just disappear into thin air sadly.
Where they are all due to notifications i.e. in return for requests rather than gifts there isn't anything you can do about that but be more sparing with the requests or faster with using materials as they arrive as 10 is the max you can "store".
The message centre allows a small very short term holding area in that it will allow you to hold off accepting the gifted items that appear at the top of the list and what I do now is clear the notifications and provide al the help in the MC first then close it down and check what things are ready to build and/or which additional items I can safely accept before doing any upgrades and repeating the proceedure accepting those items that are now back below 10 again.
This wont get round all the problems but over time I am finding that getting to know how it all functions and especially who helps with items most and so gets my urgent requests because I can rely on them turning up and who gets left more as a backup once the main helpers responses are in and I know what I still need/want. The advantage here is one isn't making 100's of requests and sitting back but sending out smaller groups of specific requests and keeping an eye on what I still need. It's hard work but for me is part of playing the game.
But then I'm a geek with far too much time on my hands. LOL
Oh and as I already said it was a very small straw you placed and as ever don't sweat the small stuff all is cool now I was just having a crap day was all.