The following two issues (tested in R7RS mode with version 0.99) may be related:

(import (rename)) gives:

Error: unhandled condition:
Compound condition has these components:
#<record &who>
    who : rename
#<record &message>
    message : "Invalid form"
#<record &syntax>
    form : (rename)
    subform : #f

As soon as rename is defined at the REPL, the import works.

rename cannot be defined in library bodies. For example, (define rename 'a) in a library body gives:

Error: unhandled condition:
Compound condition has these components:
#<record &who>
    who : define
#<record &message>
    message : "Redefinition of identifier in body"
#<record &syntax>
    form : (define rename 'a)
    subform : rename