Weird behavior with multiple textearea

Context

Edit page containing multiple textareas. Each text areas use the Wymeditor as for HTML editor.

Behavior

Trying to apply an HTML tag, let's said strong to a portion of text move the page to it's top and do not apply the desired effect. User cannot add effect to text.

• This behavior occurs on all textareas but the first.
• This behavior occurs both on Firefox and Safari latest versions.
• This behavior does not occurs with Garland Theme. That's why I create this issue.