The EU-funded project "Supporting Mathematics and Science Teachers in Addressing Diversity and Promoting Fundamental Values" (MaSDiV) (2017-2020) promoted inquiry-based learning as a pedagogy that supports diverse and multicultural classrooms. This project included the design of a professional development (PD) programme for teachers. This paper explores the mismatches between acts of promotion and offering in this PD programme when it was implemented in Malta with mathematics teachers. Findings suggest that a promotion-offering mismatch, especially when a PD programme forms part of an international project, is: (1) inevitable in view of the personal interpretations that participants construe from the texts that promote the programme; and (2) costly for everyone involved and for the quality of the PD experience itself. These results position mismatches as unwelcome occurrences. While it appears impossible to eliminate mismatches completely, the argument is made that the costs of mismatches could be mitigated by developing PD content and adopting a PD model that would increase the possibilities that the implementation of a PD programme maintains fidelity to the programme's principles. This calls for an approach to PD programme development and implementation that recognizes mismatches as a reality to be factored in from the design stage onwards.