Version 3.50 lets DTR stay at the default level that Windows sets it to. Version 3.59 explicitly deasserts DTR when the COM port is opened. This is part of a workaround we had to implement to get around a bug in the DTR and RTS handling in the Windows USB COM port driver.
As more and more people are resorting to using USB to RS232 cables it is important that DTR and RTS function correctly, despite a bug in the Windows implementation of the COM port driver used for these cables.
Andy