Problem adding \hline\noalign{\smallskip} to a tabular environment

[bersbersbers]

Comparing these two files (attached) creates something non-compilable with default settings:
a.txt
b.txt

\documentclass{article}
\begin{document}
	\begin{table}
		\begin{tabular}{l}
			X
		\end{tabular}
	\end{table}
\end{document}

\documentclass{article}
\begin{document}
	\begin{table}
		\begin{tabular}{l}
			\hline\noalign{\smallskip}
			Y
		\end{tabular}
	\end{table}
\end{document}

The output is this, and I think the problem is the deleted content in front of \hline\noalign{\smallskip}. In line with this, the error message is ! Misplaced \noalign. \hline ->\noalign

\begin{document}
	\begin{table}
		\begin{tabular}{l}
			\DIFdelbeginFL \DIFdelFL{X
		}\DIFdelendFL \DIFaddbeginFL \hline\noalign{\smallskip}
			\DIFaddFL{Y
		}\DIFaddendFL \end{tabular}
	\end{table}
\end{document}

\newcommand{\DIFdel}[1]{} fixes this, but with default settings, compilation fails.