If it takes from many addresses the fee is higher. Well I don't know exactly how it works but I have seen that fee's depends on addresses and number and amount of incoming transactions..
If you try to choose manually the source the fee will be always the same.
Not sure what you mean by choose manually.
I tried several more times than I took screenshots, and the fee constantly changed. It would even add a fee for 15k, but not 20k or 30k. It made no sense at all.
I even got 'too large' trying 300k, but it would allow 500k.
Something funky is going on...
Can anyone else do some testing and see if you get the same results? You can test without sending coins, you click cancel after it tells you what the fee will be.
then at send you will see coin control features.
if you choose input you will find all addresses that holds coins for you.
there you tick the one you like to use for sending.
check one and you will see the results at send