Given there are 2048 words in the list of valid seed words... and 12 words in a seed... the number of combinations is "very large"
You will find the next button "appears" whenever you put any valid seed in... but there are literally millions of millions of millions of valid seeds, good luck "cracking" that...
As addresses are based from the seed, it is highly likely that it let you put in the seed without custom words but the generated bitcoin addresses and private keys would have been different.
I don't quite understand what you mean by "logon" using your seed?
You are supposed to use your seed once when setting up the wallet, then you add a password (and optionally encrypt the file with your password)... when you want to open the wallet and/or send transactions, the app should ask for your password... but you certainly don't need your seed.