Steps to reproduce:

1. Create interface with combined requests enabled
2. Create 2 SNMPv3 items with for combined request
3. Create several walk[oid] items
4. Press execute now for all items

Result:

Notice that some walk[oid] items are not collected despite execute now.
In my case it was 100 walk items and 2 simple oid items

Expected:
walk[oid] items should not be collected in bulk because only first item from bulk is used in that case  (code expects only one walk, if there are several at one moment then it checks only one)