Stock Transport order does not return as PO in APO

[NRANGELOVA]

Dear friends,

I face a little bug, which I could not reproduce in our test environment.
All master data settings look great on a first check. Creating a STO in TLB the order transfer to ECC and should return as a Purchase order - in most of the created orders it is ok. But sometime instead of PO, order returns as a purchase requisition?!!
Have you met such problem or do you have an idea, what could be the reason?

Thanks in advance,
NR