Form Hierarchy Issue
Let's assume we have a form called "Form A" (reusable, not directly associated to an activity). Let's say this form has some logic in "Actions & Validations" that makes a field editable or not.
If we reference "Form A" from "Form B" and we make it readonly, then, during execution, "Form A" still executes Actions & Validations and the field is editable even though its parent field has made the whole "Form A" readonly.
This behaviour is also seen when "Form B" is a process Summary Form.