Odoo 8 many2many field outside form when visible - many-to-many

Question

I developed a module that creates a songbook on-the-fly. Based on the song_id it loads the verses of that song in the next many2many field. Sometimes, a song does not have verses and in that case the field is not visible.
<page string="Liturgy Morning">
<field name="liturgy_morning_line">
<form string="Liturgy Morning Lines">
<group>
<group>
<field name="song_id"/>
</group>
</group>
</form>
<tree string="Liturgy Morning Lines" editable="bottom">
<field name="sequence" widget="handle"/>
<field name="song_id" options="{'no_quick_create':True,'no_create_edit':True}"/>
<field name="has_songverses" invisible="1"/>
<field name="songverse_ids" widget="many2many_tags" options="{'no_quick_create':True, 'no_create_edit': True}" domain="[('song_id', '=', song_id)]" attrs="{'invisible':[('has_songverses','=',False)]}"/>
</tree>
</field>
</page>
Note the "attrs="{'invisible':[('has_songverses','=',False)]}"" in the code. The model has a field 'has_songverses' which checkes if a song has verses or not. In case the song has no verses the field is invisible.
My issue is as follows: in case a song has verses the many2many field with song verses is loaded outside the form (see attached screenshot). IMAGE:
many2many field with song verses is loaded outside the form
If I click again in the form the field is correctly rendered inside the form.
Does anyone have a solution for this issue?
Thanks in advance!