Vendor device class: packets sent before close() re-appear after interface is re-opened

[ccattuto]

I wrote an application loosely based on the webusb-serial example, that transfers small packets of sensor data, ~10 packets/s, from a USB dongle (nrf52840-mdk) to the host computer via the vendor endpoint. Just like in the example, I simulate the CDC_REQUEST_SET_CONTROL_LINE_STATE (0x22) via controlTransfer() to ask the device to start/stop transmitting data to the host.

Possible problem. IF the following happens (host side):

1. I stop an ongoing data transfer ('request': 0x22, 'value': 0x00), release the interface, and close it. I wait for several seconds up to minutes.
2. I re-open the same interface, claim it, ask the device to start data transfer with a request 0x22 with value 0x01
   THEN on many occasions the interface spits out packets that were transmitted by the USB dongle before 1) happened, i.e., across closing and re-opening the interface. They don't appear to be packets left in TinyUSB's ring buffer for the device class (I've tried modifying the TinyUSB code to clear that buffer), so I wonder whether this is a TinyUSB issue, an issue with the USB driver of the host computer (OSX), or something else entirely.

Note 1: tud_vendor_write_available() is used to make sure the device can actually send data.
Note 2: this does not happen if 1)and 2) are done on a CDC-ACM endpoint.

Thanks in advance for any insights on this.