When I explode a group or solid group, whatever tag was applied to that group, becomes applied to every raw geometry that was a part of that group.
Since all raw geometries (or whatever you call them) are always supposed to be Untagged, I would think any tags would disappear, so that all raw geometries will remain Untagged. It seems backwards that the default is for all the raw geometries to get the tag.
Yes, Dave, you can quickly and easily make them all Untagged. The point of this post is simply to share my perspective since it seems like SketchUp is working against itself here.