The web-based service (WBS) composition, e.g. mashup, is becoming a popular style to assemble web services. Numerous web-based services are developed by independent organizations and individuals due to the open nature of Web and SOA. As a result, when these components are assembled, the undesired interactions will take place and bring negative impacts. From the perspective of the feature interaction problem (FIP), we study such undesired interaction problems in WBS composition. We illustrate three WBS FIP cases and explain how on-the-fly characteristic, the significant feature of WBS composition, brings new challenges and opportunities to FIP detection and resolution.