Block indent always relative to top of file?!

I'm creating a Formatter for language that has basically two types, A and B, and looks like this:

A B
   B
   B
A B
...

Lines with A should start at the beginning of the line, lines without A should be indented.

My Psi tree starts at PsiFile where all children are a mixture of WHITE_SPACE, CRLF, A, and B. B has subchildren.

I've created blocks for A, B, and all children of B.  My indent function for my blocks looks like this:

@Override
public Indent getIndent() {
    if (this.getNode().getElementType() == B) {
        return Indent.getSpaceIndent(4);
    else
        return Indent.getNoneIndent(); // applies to A and children of B
}

The problem is that the formatter will always indent all selected lines relative to the first line in the file, so indentation breaks if the file starts with a "   B" line.

What is wrong here?  This almost looks like a bug ...