As all tech husbands and partners know, it's in your best interests to make sure your better half's tech works correctly.
So, being that I had to move the wifey's phone to CM11 to make BLN work, I thought it would be a good move to put mine on CM11 as well (so that it can be the test monkey when I have to perform trial and error to make something work).
So - we're both merrily using our CM11 loaded devices when we realise we can't restore messages using good old SMS Backup+.
As it turns out, Google has changed the SMS database security on KitKat and by default SMS Backup+ won't be able to write correctly to the Messages database.
So, scouring the internet revealed a lot of people recommending "join the SMS Backup+ community on Google+ and then you'll be able to access the Beta program which will fix the issue".
Well, that beta program seems to no longer exist.
So, what do you do?
Head over to the play store and grab yourself a copy of AppOps.
Make sure you use the one with no space in the name.
This program allows you to change an applications permissions to ensure it will work correctly for you on KitKat.
Be aware that you will need root access on your phone (not an issue if you're on CyanogenMod as it has root automagically - even if you're on a stock ROM, rooting is sooo easy these days!).
As it turns out, SMS Backup+ isn't given the permissions it needs to do it's job properly on KitKat by default.
So, once installed, fire up AppOps and scroll over to Personal.
Select SMS Backup+ from the list and scroll down to Write SMS DB.
You will notice that by default this is set to Denied.
Set it to Allowed and kick off your SMS Backup+ restore again and you're back in business.