Component autoEl iframe not saved

Using SA 3.0.4.1386, I am trying to create an autoEl-Component inside a Window.

Sometimes it is saved, sometimes it isn't

It saved correctly when I set autoEl to

{

tag:'iframe-'

}

but it did not save correctly when I set autoEl to

{

tag:'iframe',

url:'index.htm'

}

Instead, it was reverted to the previous value.

Then, when I change it to

{tag:"iframe"}

it is saved as

{tag:""}

Please help me to get it running!