In this work we explore how the use of dynamical model atmospheres has an impact on the chemical abundances derived in O-rich (massive) AGB stars. In particular, we study the effect on the Rb and Zr abundances derived from the resonant 7800 Å Rb I line and the 6474 Å ZrO bandhead, respectively. Interestingly, our new Rb abundances, including a stellar wind, are much lower (by 1-2 dex) in those O-rich AGB stars showing the higher circumstellar expansion velocities, while the new Zr abundances remain close to the solar values. The Rb and Zr derived here significantly resolve the problem of the present mismatch between the observations of intermediate-mass (4-8 M⊙) Rb-rich AGB stars and the AGB nucleosynthesis theoretical predictions.