When an RDP order is sent whitout bound it is supposed not to be clipped (practically clipped to screen). The clip is resetted to screen after each batch of bounded drawing orders. But when you resize rdesktop window through rdp_process_bitmap_caps this clip was left to the old screen size by ui_resize_window. Thus the first batch of orders is clipped at the old window size, which is a concern when you resize to a larger window at part of the window won't be redrawn.
Windows XP RDP client does behave correctly in this case and does not clip data to the old window size, contrary to rdesktop.
This one line patch correct this problem by calling ui_reset_clip() in ui_resize_window().