seed input is ignored at world creation, giving a random seed

In both 20w20a and 20w20b, when I input the world seed at world creation I get a random seed each time. I attempt to create a world with the seed 'raphael' and ensure I include said seed in the seed text box. Each time I've tried thus far I've been making it as a creative world, and the issue occurs whether or not I adjust the game rules of setting time and weather to false. I have adjusted no other values or settings, with the actual only difference being the name I give the particular world attempt.

The included attachments provide two attempts at world creation in 20w20a, displaying the main creation page, the more world options page (aka the seed input), and an image displaying the resulting seed value. In addition, I included the launcher log covering the two attempts.

(To ensure I wasn't just having a brain fart today, I attempted the world creation in 20w19a and it performed exactly as expected, creating the world with the correct seed. If I'm doing something silly, it's gone completely over my head.) As an aside, I'm unable to select 20w20a in the Affects Version/s section.