We studied the case of transparent word labels (e.g., “push”) placed on glass doors, when viewed from the other side as mirror-reversed script, hence requiring an action opposite to word meaning. As compared with a regular view, labels seen “from the other side” in the glass door situation caused strong delays of actions and a tripling of error rates. This problem is unrelated to mirror reading but is at least partially due to the need to act opposite to word meaning. The glass door effect was not related to practice and age and showed no adaptation effect after incompatible trials. Distribution analyses showed an increased correct reaction time (RT) effect for slower responses, whereas accuracy effects were specific for fast responses. In the literature, problems with such mixed mappings have often been interpreted in the sense of competing action tendencies. Experiments 1 to 4, however, demonstrated that this might merely be a task difficulty effect due to the necessity for a mental transformation in case of mirror-reversed labels. Moreover, our results strongly advocate against using transparent labels because they may pose a considerable risk.