Another possibility is that perhaps there is more than one JSR calling the routine. You can search for U:4 to see if there are any more.
As Mispeld mentions, you can configure the PLC-5 to have more than one Main Control Program (MCP). LAD2 is an MCP by default, but I think you can manually configure up to 16 MCPs in the Processor Status. If I recall, the tab is called MCP. But I don't have it open to be certain.
OG