Issuing an update against an updatable view with an instead of trigger that uses a view column in a set expression will fail at runtime saying that a reference to the value cannot be found.

for example with a gx view: update gx set x = x || 'a' where y = 2

would result in:

org.teiid.core.TeiidComponentException: TEIID30328 Unable to evaluate x: No value was available
at org.teiid.query.util.CommandContext.getFromContext(CommandContext.java:501)
at org.teiid.query.eval.Evaluator.internalEvaluate(Evaluator.java:696)