Consider files

foo-runner.scm:
(import (foo)
(scheme write))
(display (bar))

foo.scm:
(define-library (foo)
(import
(scheme base)
(ice-9 regex))
(export bar)

(begin
(define (bar)
(make-regexp "a"))))

Running this with guile -L . foo-runner.scm, yields error
foo.scm:1:0: In procedure bar:
Unbound variable: make-regexp

It seems using other libraries is fine; eg it works if I change foo.scm to
(define-library (foo)
(import
(scheme base)
(ice-9 match))
(export bar)

(begin
(define (bar)
(match "a" (_ "bar")))))

It also works if I try using regexp from application instead of module; eg if I change foo-runner.scm to
(import (foo)
(scheme write)
(ice-9 regex))
(display (make-regexp "a"))

I'm running version 3.0.5, installed through debian testing branch package manager