Reading an inactive field on sparse snode sometimes have non-zero value.

[identxxy]

When I do for loop across a sparse field, which is like projection, I can get

However, when I manually query the field, which is like ray marching, I get

This issue only occur on some sparse field, not all, but it is hard to find a certain simple case with this issue...
Any help or suggestion why this could happen?

Here is a clearer demo of the issue. The basis is a field with the hierarchy root => pointer => pointer => pointer=>dense=>field.
There is no deactivation on the sparse field. The activation should also be in correct order.

The kernel to check activation

@ti.kernel
def check_activation(self, f: ti.template(), xi: ti.i32, yi:ti.i32, zi:ti.i32) -> bool:
    ancestor_idx = ti.rescale_index(f, f.parent(2), [xi, yi, zi])
    return ti.is_active(f.parent(2), ancestor_idx)

Printing in gui

                voxel = basis[self._debug_voxel[0], self._debug_voxel[1], self._debug_voxel[2]]
                gui.text(f"voxel : {voxel.sigma} {voxel.color}")
                activation = self.check_activation(basis,
                                                   self._debug_voxel[0],
                                                   self._debug_voxel[1],
                                                   self._debug_voxel[2],
                                                   )
                gui.text(f"activation : {activation}")

Here the inactive voxel also have non-zero values.

[identxxy]

The above screenshot is taichi 1.5.0 with ti.cuda backend.
[Taichi] version 1.5.0, llvm 15.0.1, commit 7b885c28, win, python 3.9.13

If I go back to 1.2.1,
[Taichi] version 1.2.1, llvm 10.0.0, commit 12ab828a, win, python 3.9.13
it has the correct result.

[ailzhang]

@identxxy is it possible to have a minimal repro for this issue so that I can run on my side? Thanks!