The value of the custom fields created cannot be modified in the "Task Action..." menu.
Would be faster and easier for the user to change the value directly from there.
I have a custom field called "Percent done" (percent of the task done). The programmer fills the progress of the task from "Task Action..." menu and then he needs to go to edit the task and change the percent field there.
Would be great to have all the custom fields there or maybe better to define a new attribute to add the custom field to the "Task Action..." or not (like the search attribute).