Visiual Bug With Glass Panes

I've noticed that the glass panes seem to act up and won't connect (see picture below). I don't know if it is only on specific servers but I know it definitely happens with the server BeanBlockz (mc.beanblockz.com) I don't know if this can be fixed or if the panes are intended to be this way but if it is a bug and it can be fixed that would be very appreciated!