Can't type in Select2 dropdown input search field (http://kevin-brown.com/select2/)

As indicated in https://github.com/select2/select2/issues/600#issuecomment-102857595

You need to specify modal dialog element as parent for select2, that will make sure focus remains with the modal even though you have clicked on select element

$("#sRelease, #sReleaseCandidate").select2({
    tags: true,
    dropdownParent: $("#modelDialog1")
});

If you're using Bootstrap Modal then just remove tabindex="-1" from the bootstrap modal attribute. In my case it worked very nicely.