RichTextEditor 12.3.0: custom tab stops (Block.TabStopPositions) are saved but not used in layout

[Phrediac]

I’m using the commercial RichTextEditor package (Avalonia.Controls.RichTextEditor / Avalonia.Controls.Documents 12.3.0, on Avalonia 12.1.1) in a writing app and I’d like to add a Word-style ruler for tab stops. Before building it I checked whether the editor honours custom tab stops. It stores them, but text doesn’t line up at them.

I found that Block.TabStopPositions can be set on a Paragraph, and it survives an RTF save and reload (\tx900 \tx3300 \tx5700 for 60, 220 and 380 DIPs).
In the editor, a tab in a paragraph with custom stops advances by the same fixed step as a tab in a paragraph without them.
Applying the property through editor.Selection.ApplyPropertyValue(...) made no visible difference either.

Code:
var doc = new FlowDocument();
var p = new Paragraph(new RichRun("X\tat 60\tat 220\tat 380"));
p.TabStopPositions = new double[] { 60, 220, 380 };
doc.Blocks.Add(p);
doc.Blocks.Add(new Paragraph(new RichRun("Default:\tA\tBB\tCCC")));

var editor = new RichTextEditor { AcceptsTab = true, ShowToolbar = false, Document = doc };
// Both paragraphs tab identically.

I'd appreciate any help with the following questions:
Is laying out TabStopPositions planned for the editor? Or is there a setting I’ve missed?
If it is planned, will tab alignment (left/centre/right/decimal) and leaders come with it? At the moment they only survive as DOCX/RTF metadata.
In the meantime, can the editor’s default tab interval be changed?