Broken x-axis encoding for bar mark without y channel. Stack error?

[jheer]

Consider this example spec, which uses a binned x-domain and no y encoding. The result should be bars that fit the data domain and use the full group height. However, the x-axis domain is way too large, which appears to be the result of an automatically added but inappropriate stack transform in the output Vega spec. This error appears to have been introduced with the VL 5 release.

In Vega-Lite 4, the spec above worked without any explicit stack property. To get this to work in v5 I have to add an explicit stack: false, as in this example.

Note that this bug is preventing me from seamlessly porting a Crossfilter example on Observable to VL 5.