Does it hash src addr/dst addr/ports ? Or other method ?
I have tested and single TCP connections and it get switched during transfer between interfaces, so looks like it's like some round-robing algorithm not related to identified flow.
Is it correct MT behaviour/implementation or some bug ?
I use ECMP on identical link (in terms of link length, speed, MTU), however according to RFC2991:
If the parallel links are identical, then most of the
concerns discussed in this document are avoided with the combined
link. The exception is packet reordering, which can still occur with
round-robin, adversely affecting TCP.