Bean seed saving

I always save some seeds from my french beans (climbing & dwarf) because I didn’t think they cross. I’ve just been reading the beans & herbs website. https://www.beansandherbs.co.uk/unusual-...bean-seed/
 That says climbing beans should be planted 10m apart to prevent crossing. I’ve never done this. They have always grown next to each other in the same bed. 
Have I been growing weird mutant beans for the last few years? The beans look the same as what I planted originally. I wouldn’t have saved them if they’d looked different.

I found some of my saved DFB came up a bit weird, so I assume they crossed. Not got the room to isolate all my different varieties so I'll have to take the risk.

I always grow mine together too. Real Seeds says:

"French beans are self-pollinating, mostly before the flowers open. Despite this, they can be crossed by insects with other varieties nearby. The extent of crossing varies by area. If you are just saving seed for your own use, grow your seed crop of french beans at least 6 feet away from any other variety (12 feet if possible), and you are unlikely to have a significant problem with crossing in the UK."

I'm not really following that advice either, but there we are. A bit closer to my reality and probably sufficient for my needs as a non-supplier. I'll bin anything that looks dodgy (or will I grow it out of curiosity?) but like JJB I'll just take the risk.

I will have two growing areas, so I will try to keep them separate this year if I can. And if I can remember lol

I bought three varieties of climbing french beans from Beans&Herbs last year and two varieties had clearly crossed with borlotti beans when I grew them last summer.

Some of the beans were correct however so I'm going to try them again this summer to see if they come true.