Hyundai handbrake.

Do a decelerometer test 15 mph in reverse and record your results lol same for a bike also I think.

Have you got a handbrake on your bike, no , It was a light hearted poor attempt at comedy, but seriously we do not test the park brake in reverse and I have come across many vehicles that have greater problems holding when facing uphill rather than facing downhill.
The Hyundai ix20 is know to have issues that you describe and is worth adding an advise if you are aware of it being a likely problem.

some bike's do have a handbrake,mainly the cheap chinese copies of 125's,it's a little flap you push down when you squeeze the rear brake lever and it keeps the lever locked,obviously not part of the test,not having a go,just to inform you.....lol

Yes thanks for that, problem is I didn't see the car so not sure what model it was 🙄

Please take the time to read my post fully ht .....

You will see I asked a question.

Thè aim was to elicit knowledge from those who may have experienced the same scenario.

OK I'll spell it out.

Anyone come across a Hyundai where the handbrake works fine when the wheels are in the forward rotation but does jack sh*t when the car is parked pointing uphill.

Hope that's clear enough.