Hi,
I can reproduce this on 1.9.0 but it seems to be fixed on master.
# !pip install --pre torch -f https://download.pytorch.org/whl/nightly/cu111/torch_nightly.html
print(torch.version.__version__) # '1.10.0.dev20210723+cu111'
class TensorFoo(torch.Tensor): pass
tensor = TensorFoo([1,2,3,4]).requires_grad_()
print(tensor.is_leaf, tensor.requires_grad) # True True

As a workaround, you can use tensor._base