The question, as mentioned in the title, is what causes the tx option field with the value 0x01 (disable ack) exactly. I assumed it disables the aps layer acknowledgement and the additional aps retries. But they occur in any way with aps acknowledgment disabled, too. The retry counter of the tx status frame counts still, sometimes till 60. I think this is a bit too much for the mac layer retries. Or there are also retries in nwk layer?
the Option 0x01 on TX Request (API frame) doesn't disable the acknowledgment, it does disable the retries (up to 3). The following is a example of a TX Request frame with retries disable:
7E 00 0F 10 01 00 13 A1 00 40 AA D0 06 FF FE 00 01 04 78
For you to disable the acknowledgement you need to set 0x00 on Frame ID of TX Request. Here is an example:
7E 00 0F 10 00 00 13 A1 00 40 AA D0 06 FF FE 00 00 04 7A
I guess the Transmit Retry Count (from ZigBee Transmit Status frame) is related to CSMA-CA.