I apologize in advance for all the pictures, but they are needed to show this...
While messing around with the wallet today, I found out that transaction fees are randomly added whether you have it specified in your settings or not, the amount you try to send doesn't matter. Wallet version v3.0.3.0-g354c0f3-MultiAlgo (64-bit)
In my wallet, I have it set to not add a transaction fee:

So, I set up a test to send 50k and a transaction fee was added:

I tried it with a little bit less and there was no fee:

I checked it with 100k and the fee is 4x more than sending 50k:

What about 200k? almost 10x more of a fee than 100k:

Now something really strange happens, I cancel and try again, same amount, and the fee changes!

Let's try alot more coins. Why is the fee less?

What happens if I try to send over a million? It won't let me:

Can anyone explain this?