Understanding spi_buf_set SPI behavior

Question

Hi, 
 
 I am controlling an external device using SPI(M), SYNC, with the nRF52840 DK. 
 I am using the exact same GPIO configuration using two different test apps using SDK16 and NCS. SDK16 works as expected, the NCS has strange behavior. 
 With NCS, I have everything about the CS working, defining a special overlay to control CS and the extra GPIO signals from the Arduino type shield that I am using, and it does everything with no errors. 
 Now, my question is the following: When you have buffer sets that are not the same length the TX and the RX, I followed the code on the spi_nrfx_spi.c driver and it would seem as if it is a loop sending each pair of TX, RX bufs, using transfer_next_chink(), until the last one up to the bigger count in the spi_buf_set would be exhausted, placing ORC chars where needed in each TX-RX bus pair if they have different length. 
 But what I observed is totally different. All tx bufs are set contagiously, the same as all rx, and it behaves like a concatenation of tx and rx. 
 So, which is it, doing transfers of each tx-rx pair in the set, using ORC to fill the gaps of the shortest ones, or a concatenation of all the tx, and the rx, and just doing one transfer? 
 Unfortunately the documentation is not clear about the internal behavior of uneven lengths on the sets. 
 I am placing some code to exemplify my question. 
 void read_registers( u16_t address, u8_t *buffer, u16_t size )
{
 u8_t cmd = READ_REGISTER;
 u8_t addr[2] = { ( address & 0xFF00 ) >> 8 , address & 0x00FF };
 u8_t nop = 0;
 u8_t filler[4]; 

 struct spi_buf tx_bufs[] = { { &cmd, 1 }, { addr, 2 }, { &nop, 1 } };
 struct spi_buf_set tx = { tx_bufs, 3 };

 struct spi_buf rx_bufs[] = { { filler, 4 }, { buffer, size } };
 struct spi_buf_set rx = { rx_bufs, 2 };

 int ret = spi_transceive(spi, &spi_cfg, &tx, &rx);
 CHECK_ERR_NO_RET_VAL(ret, "read_registers()");

 if(size == 1) {
 LOG_DBG("RD REG cmd:0x%02X, addr:0x%02X%02X, buffer:0x%02X, size:%i", 
 cmd, addr[0], addr[1], buffer[0], size);
 } else {
#if CONFIG_LOG_DEFAULT_LEVEL == LOG_LEVEL_DBG
 char buf[40];
 sprintf(buf, "RD REG cmd = 0x%02X, addr:0x%02X%02X", cmd, addr[0], addr[1]);
 LOG_HEXDUMP_DBG(buffer, size, log_strdup(buf));
#endif
 }
}
 
 Thanks!