Have you try Jedi Mindtricks? Wave your hand and say "you can not see me" : D

I think you can make yourself invisible in your dreams, if you wish so and know that you are invisible. But still, our mind can have a plan of it's own and it does do things we would not expect.

The belief is, that our dreams behave based on our thoughts, intent, fears... But no clue what is happening when dream behaves unexpectedly.

Also, maybe we are sometimes not in a simple dream in our head or in our private dream area. But in a public space, where other dreamers or entities can be and rules are different.

Moving this to Dream control