SO I started up with nano-wallet and created .wlt file upon request to do so upon initialization/download of wallet and running the start.html. Then I deposited coin and later on used the backup feature which created a .wlt encrypted version of private key which was now DIFFERENT. It had the same 80% as the first version, but omitted the last 5 characters and the last character which was a single equals sign ‘=’. Then it added about 500 more characters and ended with two equals signs ‘==’ So to be sure, with zero confidence in the .wlt file - I copied the ACTUAL private key to a file. Be aware of this everyone. If it happens to you, you MUST have your actual 64-character private key displayed on your nano-wallet so you can print it. Anyone else can confirm this happened to them? It is easy to miss because the first 80% of the encrypted key looks the same! the last 5 characters are omitted and about 500 chars. added and then two equals signs. To repeat myself 
Thanks everyone, and good work in the NEM community!
Hi,
No worries, it seems that when wallet is backed up from the account page it adds a few $$hashKeys to the object, like:
"$$hashKey":"object:152"
Angular adds this to keep track of the changes. Private key is still safe and wallet will work.
Will fix that in next version.
Hi,
Just started with NEM the other day and became aware of this. The .wlt file I got when I first created the wallet has about 100 characters less than the backup file I downloaded later from the wallet account. I tried with a new wallet just to test if it would happen again and it did. The changes that occurred in my file are different than the ones kensilverman1 described. In my case only around 70 characters were added after having removed the last 5 characters of the initial file. Can I be sure this will only happen once? Now after having put some coins in there the backup file available for download is identical to the second one I downloaded. I have saved both versions and the private key but it has created a certain amount of doubt, especially now when there is money in it.
Will I be able to use either of them for an eventual recover of the wallet in the future?