Trigger-Action Programming (TAP) has been shown to support end-users' rule-based mental models of contextaware applications. However, when desired behaviours increase in complexity, this can lead to ambiguity that confuses events, states, and how they can be combined in meaningful ways. Blocks programming could provide a solution, through constrained editing of visual triggers, conditions and actions. We observed slips and mistakes by users performing TAP with Jeeves, our domain-specific blocks environment, and propose solutions.