What may be happening is that the field is accepting the InputID value variable as a rowlink (or picklist). So your first formula may be deleting the specified rowlink in the Customer table, but would need more specification in the other table of where to locate the matching ID.
This means that for your second formula, you would need to also specify the column of the ID value to match that given row link.
So the second formula would look something like this: =FINDROW(CustomerID, "CustomerID[ID]=$[InputID][ID]")