Elisp manual node Special Properties says this about `intangible':
If a group of consecutive characters have equal and non-`nil'
`intangible' properties, then you cannot place point between them.
If you try to move point forward into the group, point actually
moves to the end of the group. If you try to move point backward
into the group, point actually moves to the start of the group.
When the variable `inhibit-point-motion-hooks' is non-`nil', the
`intangible' property is ignored.
It does not say anything about what the meaning or behavior is if
consecutive characters have unequal but non-nil `intangible'
values. Why the qualification of having equal values? What is a user
to understand about this?