workflow not working for multiple line items

Hi gurus,

we are working on ECN/ECO workflow.

Once ECN is created in CC01, our workflow triggers.

we are calling subflow from main WF for enhancing the materials of the Engineering change number(ECN).

Subflow will take the material to different departments for enhancing the views like,

Purchasing views by purchasing dept,

quality views by quality dept,

sales views by sales dept,

etc.

This whole process is working fine, if there is single material number in ECN.

But, if there are 2 material numbers, the control is not returning back to MAIN WF from Subflow.

do we need any config/setup to make it work. (we are using block while calling subflow).

Any help will be of gr8 use.

rgrds.

santosh.