Width of select2 input is getting smaller when bootstrap panel is open by default

Is this a bug?
#1

Inside a bootstrap panel I have a form where I use select2 for select inputs.

The problem is that when I define the panel to be closed by default (by removing the in from the class="panel-collapse collapse" ) the width of the select2 input is getting smaller!

I have posted also in stackOverFlow where I have posted an example…

Thanks