I have a tree-like data structure (with cycles)

Show (has many) submissions
Submissions (has one) prices and (has one) artwork
Prices (has one) Submission and (has one) artwork

(aka the price points to both the artwork and the submission)

I create a new submission/price pair in the .xhtml page

<a:commandButton id="addANewSubmission" value="Add New Submission"
 action="#{showsHome.instance.addSubmissionPrice(submissionHome.createNewPricelessSubmission(), priceHome.createNewPrice())}" reRender="ajaxSubmission"/>

which calls

 public void addSubmissionPrice(Submission newSubmission, Price newPrice) {
 this.submissions.add(newSubmission);
 newSubmission.setShows(this);
 newSubmission.addPrice(newPrice);
 }

Everything works fine if I don't have a price (which is optional) any idea on what I'm doing wrong? Any ideas would be appreciated.
BTW here's the complete error

Exception during request processing:
Caused by javax.servlet.ServletException with message: "#{showsHome.persist}: javax.persistence.PersistenceException: org.hibernate.PropertyValueException: not-null property references a null or transient value: com.rdfsg.artdb_seam2.Price.submission"

javax.faces.webapp.FacesServlet.service(FacesServlet.java:256)
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:83)
org.jboss.seam.debug.hot.HotDeployFilter.doFilter(HotDeployFilter.java:68)
etc

Thanks