Weird Spacing around Bold Text when using Custom T1 Fonts

Update 2016/12/10

A new version of mweights.sty has been uploaded to CTAN and deployed in TeX Live, with release date 2016/12/09, which seems to solve this and all other related issues.

Original answer

The last update to mweights.sty introduced some unprotected end-of-lines.

\def\mweights@init{%
% Define any undefined \mdseries@rm etc. 
% Defined \mdseries@rm etc. assumed to be fully expanded!
\ifdefined\mdseries@rm\else\edef\mdseries@rm{\mddefault}\fi
\ifdefined\bfseries@rm\else\edef\bfseries@rm{\bfdefault}\fi
\ifdefined\mdseries@sf\else\edef\mdseries@sf{\mddefault}\fi
\ifdefined\bfseries@sf\else\edef\bfseries@sf{\bfdefault}\fi
\ifdefined\mdseries@tt\else\edef\mdseries@tt{\mddefault}\fi
\ifdefined\bfseries@tt\else\edef\bfseries@tt{\bfdefault}\fi
% In case any unexpanded macros present in \rmdefault, etc
\edef\rmdef@ult{\rmdefault}
\edef\sfdef@ult{\sfdefault}
\edef\ttdef@ult{\ttdefault}
\edef\bfdef@ult{\bfdefault}
\edef\mddef@ult{\mddefault}
}

You can see them after the braces.

Temporary fix:

\documentclass{article}
\usepackage[default]{raleway}

\makeatletter
\def\mweights@init{%
% Define any undefined \mdseries@rm etc.
% Defined \mdseries@rm etc. assumed to be fully expanded!
\ifdefined\mdseries@rm\else\edef\mdseries@rm{\mddefault}\fi
\ifdefined\bfseries@rm\else\edef\bfseries@rm{\bfdefault}\fi
\ifdefined\mdseries@sf\else\edef\mdseries@sf{\mddefault}\fi
\ifdefined\bfseries@sf\else\edef\bfseries@sf{\bfdefault}\fi
\ifdefined\mdseries@tt\else\edef\mdseries@tt{\mddefault}\fi
\ifdefined\bfseries@tt\else\edef\bfseries@tt{\bfdefault}\fi
% In case any unexpanded macros present in \rmdefault, etc
\edef\rmdef@ult{\rmdefault}%
\edef\sfdef@ult{\sfdefault}%
\edef\ttdef@ult{\ttdefault}%
\edef\bfdef@ult{\bfdefault}%
\edef\mddef@ult{\mddefault}%
}
\makeatother


\begin{document}
There is a \textbf{weird} gap before that \textbf{bold word}. But not for \emph{italic}.
\end{document}