How can I set where Paypal draws funds for automatic payments?

[RetroStuff]

I normally pay my eBay fees as I go, but now I want to switch to letting it be drawn automatically by eBay...

...the thing is I don't know whether Paypal will draw from my bank account or my credit card if my Paypal balance is at zero when the fees are drawn.

Where do I have to look in my account to find this out?

Is there a way of setting a primary source to be drawn from under these circumstances?

[RetroStuff]

Just found it...

...it doesn't let you set primary, it just asks you to choose one and delete the other...I didn't read closely enough to realise it wouldn't remove the other payment method entirely from my whole account (at least I'm hoping it wont)...but here are some screen grabs showing where/how...

[RetroStuff]

I tried to leave just my bank account selected and it's giving me an error message...

...it won't let me set my bank account as the only funding source...it'll only accept my removing it in favour of an existing credit card.

I'm wondering if that's standard...anyone know if that's just standard, or is it a software glitch?