I am in London today, and on a whim yesterday, booked a hostel bed and came up last night, instead of getting a train at some unholy hour this morning. I booked a bed in a single sex dorm, which I thought was a women's dorm, but wasn't checking that bit so closely, as I was more focussed on checking I had the right date, which I couldn't find.
I planned to send feedback after I got back home, because the confirmation page didn't seem to show the date - I did eventually find it, but I think it needs to be more prominent.
What I hadn't been expecting was for that single sex dorm to be a male dorm, on account of me being female. No one mentioned in when I checked in and was given a room card (with a pink sticker on the back, but I don't know if it was relevant.) They spoke to me by name, and Emma seems to be universally recognised as a female name in most European countries and English-speaking ones. Plus I don't think I look very androgynous.
When I got to the dorm, there was no one else there, and I showered (single sex showers across the corridor) and went to bed and was asleep before anyone else was there. So I didn't realise until this morning that the single sex dorm was in fact male, not female.
As I was not in the room awake at the same time as anyone else, and I changed in the shower room, it wasn't an issue for me - but it very easily could have been a problem, and not necessarily just for me - after all, men should be entitled to have a men-only space if that's what they've booked, just as women should be able to expect it.
They were very apologetic when I checked out.
But I don't think it would have happened at all if the default on most computer forms wasn't male. (And if the details of what you selected was more prominent - not just the booking ref number.)