OSB xmlbeans outofmemory

we had a couple of cases of OOM lately, both preceded with this stuck thread:

      org.apache.xmlbeans.impl.schema.SchemaParticleImpl.isFixed(SchemaParticleImpl.java:203)
        org.apache.xmlbeans.impl.validator.Validator.validateSimpleType(Validator.java:1205)
        org.apache.xmlbeans.impl.validator.Validator.handleText(Validator.java:829)
        org.apache.xmlbeans.impl.validator.Validator.textEvent(Validator.java:814)
        org.apache.xmlbeans.impl.validator.Validator.nextEvent(Validator.java:244)
        org.apache.xmlbeans.impl.store.Validate.emitEvent(Validate.java:168)
        org.apache.xmlbeans.impl.store.Validate.process(Validate.java:84)
        org.apache.xmlbeans.impl.store.Validate.(Validate.java:39)
        org.apache.xmlbeans.impl.store.Xobj.validate(Xobj.java:1878)
        org.apache.xmlbeans.impl.values.XmlObjectBase.validate(XmlObjectBase.java:386)
        stages.transform.runtime.ValidateRuntimeStep.validate(ValidateRuntimeStep.java:225)
        stages.transform.runtime.ValidateRuntimeStep.processMessage(ValidateRuntimeStep.java:124)
        com.bea.wli.sb.stages.StageMetadataImpl$WrapperRuntimeStep.processMessage(StageMetadataImpl.java:346)
        com.bea.wli.sb.pipeline.PipelineStage.processMessage(PipelineStage.java:84)
        com.bea.wli.sb.pipeline.PipelineContextImpl.execute(PipelineContextImpl.java:1055)
        com.bea.wli.sb.pipeline.Pipeline.processMessage(Pipeline.java:141)
        com.bea.wli.sb.pipeline.PipelineContextImpl.execute(PipelineContextImpl.java:1055)
        com.bea.wli.sb.pipeline.PipelineNode.doRequest(PipelineNode.java:55)
        com.bea.wli.sb.pipeline.Node.processMessage(Node.java:67)
        com.bea.wli.sb.pipeline.PipelineContextImpl.execute(PipelineContextImpl.java:1055)
        com.bea.wli.sb.pipeline.Router.processMessage(Router.java:214)
        com.bea.wli.sb.pipeline.MessageProcessor.processRequest(MessageProcessor.java:96)
        com.bea.wli.sb.pipeline.RouterManager$1.run(RouterManager.java:593)
        com.bea.wli.sb.pipeline.RouterManager$1.run(RouterManager.java:591)

Doing a heap dump and using Eclipse MAT I could trace reconduct them to a org.apache.xmlbeans.impl.store.Cursor class, _toPrevBookmark method.
Still investigating.
PS it seems this was due to very large payload (> 20 MB). However it's quite frustrating.