RichText: Non-collapsed selection abruptly interrupted when spanning multiple nodes

[aduth]

When holding down the mouse cursor and selecting text in a paragraph which spans multiple child nodes, the selection is abruptly terminated.

This can happen for Shift+Enter created newlines, where the paragraph is a series of #text, br, #text nodes:

And can happen as well for text which is applied some formatting, e.g. bold:

I'm not entirely sure it's related, but in the course of this I also discovered some similar selection issues with uncollapsing a selection (via Shift+Arrows), where the selection starts to expand from the right (instead of continue contracting) when reaching the end of a formatted node.