DepthTest disabled Billboard still blends with (alpha textured) background primitive

We are using SVG images as `image` on a `Billboard`. To always render the Billboards on front we have set `disableDepthTestDistance = Number.POSITIVE_INFINITY`. It renders OK, except when a primitive with an alpha enabled material is positioned behind the Billboard. Then strange things happen where it seems white colors from the texture are made transparent, but other colors are not.


The given example is with Order Independent Transparency disabled, but also occurs with it enabled. In the example I have also reduced the number of `frustums` to 1, in order to eliminate causes related to multiple frustums, so this seems to not be the cause either.

Start by reproducing the Billboard case using an SVG image with disableDepthTestDistance set to Number.POSITIVE_INFINITY, placing an alpha-enabled primitive behind it. Compare the result with Order Independent Transparency enabled and disabled, keeping frustums at 1 as described. Done means the Billboard renders correctly without making white texture colors transparent.

Written by the indexing model from the issue text.