Paper size changes for unknown reasons

Question

I have a document that's supposed to compile in a4paper. Until recently, that worked just fine, however now it's using the same width, but a significantly increased height. It's pretty much a 2:1 ratio now.

I narrowed it down to the following code:

\usepackage[margin=2.5cm,right=3cm]{geometry}
\usepackage{mathptmx}
\renewcommand{\rmfamily}{%
\fontfamily{ptm}%
\fontsize{12}{1.5pt}%
}

When I replace this with just usepackage{geometry}, everything is back to normal.

The preamble also contains these potentially relevant clauses:

\documentclass[a4paper,bibliography=totoc]{scrreprt}
\usepackage[T1]{fontenc} % part of standard header for European documents
\usepackage[utf8]{inputenc} % part of standard header for European documents
\usepackage[babel,english=american]{csquotes}
\usepackage[USenglish]{babel}
\usepackage{graphicx}
\usepackage{tikz-uml}
\usetikzlibrary{positioning}
\usepackage[backend=bibtex]{biblatex}
\usepackage{stackengine}[2013-10-15]

(It also contains some formatting tricks, none of them changes the paper size or any existing command or length, though. Plus, I doubt it's because of StackEngine or BibLaTeX.)

I'm not sure if it's specific to the toolkit I use (PDFLaTeX with TeXLive backend and TeXlipse frontend under Windows 10) because I didn't really try it in a different environment.

What about this code would change the paper size and what should I do instead?

Answer 1

So turns out I was hallucinating the wrong paper size. What made me think it had changed was the decrease in page amount which was caused by the fact that the margin was decreased properly, but the code that was meant to increase the font size and line spacing was doing nothing. In other words, this:

\usepackage{mathptmx}
\renewcommand{\rmfamily}{%
\fontfamily{ptm}%
\fontsize{12}{1.5pt}%
}

doesn't work for changing font, font size and line spacing. The code that actually works is, in fact, much simpler: Add 12pt to the optional parameters of \documentclass and apply

\renewcommand{\baselinestretch}{1.5}
\usepackage{mathptmx}
\renewcommand{\rmdefault}{ptm}