In #2248 (comment) @MatsPalmgren wrote:

I was just updating some code dealing with min-width:auto and I'm wondering if min-width:N%with an indefinite percentage basis counts as auto in this context? In particular, does Automatic Minimum Size apply? https://drafts.csswg.org/css-grid/#min-size-auto

In #2248 (comment) @dholbert wrote:

I tend to think that it should apply, though I don't think any spec text says that it would. And really, CSS2 has text saying that for min-height (which in CSS2 was the only one of the min-{size} properties that could have an indefinite basis), it falls back to '0':

The percentage is calculated with respect to the height of the generated box's containing block. If the height of the containing block is not specified explicitly (i.e., it depends on content height), and this element is not absolutely positioned, the percentage value is treated as '0'

https://www.w3.org/TR/CSS22/visudet.html#propdef-min-height

I suspect "treated as '0'" there was really meant to signify "treated as the initial value". And so now, under that interpretation, this scenario should now fall back to auto-which-then-usually-gets-treated-as-0... This might want its own spec issue, though.

Thus, its own spec issue.