The sad part is that a very tiny code tweak to the 8u2 code could switch autoreset on the UNO from using DTR to RTS
which would mean that this autoreset on tty port open issue could be avoided altogether.
The original reason that DTR was used over RTS on the early boards was
because to use RTS required changes to Avrdude
to toggle RTS before the download started when using Arduino boards.
Whereas, DTR is asserted (it drops to gnd while the port is open) by the OS when the port is first opened
without the application having to do anything.
The cap turns the DTR drop into a pulse which is used for reseting the AVR.
This allowed auto reset to "work" without any modifications to Avrdude.
Now that Avrdude has been updated to include an "Arduino" protocol that toggles RTS to create the autoreset pulse,
there is no need to use DTR for autoreset anymore.
My view is that the USB to serial AVR chip code should be tweaked to use RTS rather than DTR.
It is a very small code change.
I prefer using RTS over DTR because it allows opening the serial port without resetting the AVR
but yet still allows autoreset to reset the AVR for uploading new code.
--- bill