In this work the processes causing a severe uplift of the baseline at elevated ion source pressures are investigated. Three hypotheses were investigated but proven wrong experimentally: i) Ion breakthrough involveing unfiltered ions reaching the end of the rod region despite being theoretically unstable. This could be caused by space charge effects owing to the elevated ion source pressure. ii) Pre-amplifier adaptation of the baseline to keep both the highest peak and the baseline within its dynamic range. iii) Photons of sufficient energy leading to the photoelectric effect on the detector surfaces. Calculations involving the ionization cross section and the excitation cross section of argon as well as DSMC simulations demonstrated the presence of sufficient excited species traversing the QMF to cause the baseline shift. The excited species themselves cannot be the main source for the baseline shift as it was established that potentials applied to the deflection plate affect the baseline significantly. This led to the proposal of secondary ions produced inside of the deflection unit to be the cause for the uplift of the baseline. It was hypothesized that the mere interaction between an excited atom and a given surface can lead to an ionizing reaction if the work function of the surface is larger than the effective ionization energy of the excited particle. A combination of Molflow and SIMION simulations as well as experiments involving the variation of applied potentials inside of the deflection unit and generated ions in this geometry are in excellent agreement, which is taken as strong evidence that this mechanism is indeed the root cause for the baseline shift. An alternative deflection unit was designed to replace the original unit and circumvent the problem as well as provide further proof that the surface indeed plays a crucial role in the mechanism. The data taken with this unit exhibit only a small amount of baseline shift which suggests a second mechanism.