First-level subtasks inherit the custom fields of their parent top-level task, but unlike the top-level task which shows all those custom fields and values by default, they are hidden until you click a Show inherited fields link (see below). Folks have complained about this because it can add up to a lot of extra clicks and a little undesired friction.
I’ve been able to resolve one of the big offenders in my workflow in a non-intuitive way, so I thought I’d share it here.
Now that My Tasks offers custom fields, you can use a side effect to help. Any custom fields you’ve added to My Tasks, if present on a subtask, will show by default in a My Tasks Fields section; no expansion required It looks like this:
While this won’t work for all cases of needing to click to expand, it may take care of some nuisance ones, as it has for me.