Scheme implementations compliant with R6RS live in a somewhat uneasy tension with a standard Scheme REPL (read–eval–print loop), which the Report effectively does not define.
In particular, the effect of reimporting a module, as you might do when reloading and rerunning a program, isn’t well–defined by R6RS. This is a limitation caused by the particular design choices made in R6RS.
Accordingly, the interactive mode is intended for quick experimenting with the built in features. It is intended neither for developing applications nor for writing any substantial piece of code.