"port_ha" drop count is increasing, ha1 and ha2 drop show 0 - why?

Hi!

As I understand, "port_ha" is virtual manifestation of physical "ha1" or "ha2" (depending on priority), so, why am I seeing its drops counter increasing but not either of latter?

<node_redacted> (root) # diagnose netlink device list | grep port Inter-|Receive                                                                     |Transmit  face |bytes             packets     errs drop      fifo frame compressed multicast|bytes          packets     errs drop fifo colls carrier compressed : port_ha:  59307243213    183676419   0    268802671 0     0    0          0        |2695447833533  2029323361  0    1    0    0     0       0 :										   |    ha2:   442088029516   531221403   0    0         0     2    0          4059668  |2709586459181  2051768332  0    0    0    0     0       0    ha1:   43740481445    77620950    0    0         0     0    0          2989697  |13166888759    21729664    0    0    0    0     0       0 :										   |

Thanks!