Migrating OWB to ODI: ORA-02292 integrity constraint (DEV_ODI_REPO.FK_MAP_EXPR_REF_3) violated - child record found

I have run into a persistent error when trying to migrate my OWB mappings to ODI. I use this simple mapping for test purposes:

When I migrate this to ODI I get the following result:

So far so good and exactly as expected. Now Expression_0 is no longer needed and has to be removed, so select the object, press delete and save. The object disappears, but the icon stays highlighted. Pressing the icon again seems to save the changes. Close and reopen the mapping, and lo and behold the expression_0 object is still present. Now delete it again and press the save all button instead and…..

Unable to save MAPPING_3 (ODI-10143: Error while accessing the ODI repository.   
ORA-02292 integrity constraint (DEV_ODI_REPO.FK_MAP_EXPR_REF_3) violated - child record found

I never used to get this error before, but I think I might just have pressed the save button and not noticed the object did not disappear. This looks like a bug in the migration utility to me.
There is a workaround, but that requires me to modify the original OWB mapping, I have not yet found a way to solve the problem in ODI.
The workaround is as follows:

• either remove the expression in OWB before the migration
• or replace the expression by a constant (you can still use expressions in a constant and since it the input for a pre-mapping it will only be evaluated once)