Comment 4 for bug 493318

> Notice that the style attribute is not "unset" on the "use"
referent "#MyPath".

Style attribute cannot be unset, only individual properties can. And in this example, the original has e.g. the fill unset, i.e. it is not specified for it. This is why setting blue fill on the use works.

I'm going to close this as invalid, please don't take this personal but it doesn't seem like you uncovered any problems here, Inkscape works according to the spec in this aspect.