I would think that Ctrl-shift-right would increase both these notes by an eighth note (current grid resolution). Instead, it only extends one. When I attempt to grab and lengthen the other, it swaps the durations.
It’s a bit perplexing and requires a workaround. Is this intentional functionality?
I’m not sure I fully understand your problem, but I find that when Dorico behaves unexpectedly I’ve often accidentally toggled (or forgotten to turn off) one of three things; Insert (I), chord input (Q), or I’ve accidentally toggled ‘force duration’.
I couldn’t find a better “solution” as untie a lower note, select both notes, increase a length and tie it again. Any way I understand - I would expect Dorico could handle with this situation without such workarounds.
This is a limitation of the currently intended functionality. When Dorico changes the duration of subsequent notes, it goes left to right, but only changes the duration of those notes that haven’t been overwritten by any previous note that has just changed duration.
This does allow for example to just select a few notes, hit the rhythm dot button, and avoid overlapping notes.
I think what’s missing here is a special case for either partly overlapping notes, or maybe just looking at chord mode, and allowing overlapping notes.