+ AA6YQ comments below
the default K3 configuration (CONFIG:PTT-KEY) has external PTT and FSK keying disabled, that applies to both the RS-232 port and the virtual USB serial port. So although it is correct to not configure Commander to try and PTT the rig via RTS or DTR if CAT PTT is being used, it will only have an effect if the rig's CONFIG:PTT-KEY option is also set to something like RTS-DTR as opposed to the default OFF-OFF
+ That makes an assumption about where the K3's "PTT lockup" defect lies. Setting Commander's RTS and DTR selectors to "OFF" eliminates any possible source of external PTT assertion.
+ If RX-TX switching via CAT command is reliable - first with Commander standalone, and then with WSJT-X - the user can then if desired change to using PTT for RX-TX switching instead of using CAT commands for that purpose. This maintains a "change only one thing at a time" approach to debugging.