Using simple_format somehow modifies a models attribute in-place

This is a weird one. I have a page that simple_format's a comments attribute on an instance of a model. However on the same page is a form allowing this comment to be updated. When I simple_format the attribute, the form then shows this attribute in it's modified form (i.e. with paragraph tags etc...).

I can't see how this is happening unless somehow simple_format is modifying the models attribute in-place but how could that happen when it is executed like this:

simple_format @warranty.comments

outputs:

<p>Here are some comments</p>

and further down the page in the form, or even if we just call:

@warranty.comments

we get:

<p>Here are some 开发者_高级运维comments</p>

If I change it to:

simple_format @warranty.comments.clone

the behaviour goes away.

Am I missing something obvious here? I'd not expect a text helper to modify the original attribute unless it was called like @warranty.comments.simple_format!

This was a bug that was fixed earlier this month. The latest 3.1.0 should have the fix, but I'm not sure about the other versions.