Global context values override local transaction context values

[roncohen]

As shown in the tests, context from the top level values currently override any local values. Local values should take precedence.

[alvarolobato]

Related #1175

[alvarolobato]

We agreed to defer together with #1175

[jalvz]

@simitt can we close this now?

[alvarolobato]

This is probably fixed, needs checking.