The class is badly written (to use understatement), I'm afraid. In 2014 it loads oldlfont, which is a package to be used only for typesetting documents written with LaTeX2.09, that's been obsolete for more than twenty years.
In the class file you find
%% WARNING: math font problems and workaround:
%% Standard math commands like
%% $\mathbf{N}(0,P(0))$
%% will not work properly. The reason is, that this is
%% a simple hack of an old LaTeX2.09 style files.
%% To get it running, I used the packages
%% 'rawfonts' and 'oldlfont'
%% They are responsible for the font problems.
%% This is a known feature, see
%% http://www.tex.ac.uk/CTAN/latex/bugs.html
%%
%% WORKAROUND:
%% Use an additional pair of braces, like
%% {\mathbf{y}}
%% to introduce an additional level of scope.
%% Examples:
%% $\mathbf{N}(0,P(0))$ but ${\mathbf{N}}(0,P(0))$
%% $\mathcal{N}(0,P(0))$ but ${\mathcal{N}}(0,P(0))$
%% $\mathcal{G}_{t}$ but ${\mathcal{G}}_{t}$
%% $\mathfrak{G}_t$ but ${\mathfrak{G}}_t$
The text is typeset using the Computer Modern math fonts along with Times for text, which is simply horrible.
The workaround would be very simple: changing \usepackage{mathptmx} instead of \usepackage{times} (that's loaded twice for mysterious reasons) and removing \usepackage{oldlfont} and `\usepackage{rawfonts}.
Changing your formula into
F={\mathrm{m}}a
produces

(notice Computer Modern for math).
oldlfontsurely{\rm m}? – Joseph Wright Sep 18 '14 at 09:27\DeclareOldFontCommand{\bf}{\normalfont\bfseries}{\mathbf}to your document preamble or change the occurrences of\bfin the class with\bfseries. My impression is that the class maintainers were bitten by\bfnot being defined and resorted tooldlfont, which is the worst thing to do. – egreg Sep 18 '14 at 12:24