compose button erases text in mail-compose

[blokkie]

When clicking the compose button again after typing a text in a new mail erases all that text again.
to reproduce :
klick compose
types some text in the body section
klick compose again
text is gone .

Expected behaviour

• text remains and is not removed
  or
• compose-button is grayed out (disabled) as you are already in compose
  or
• ???