Unwanted line breaks after equation tag when using fleqn and leqno

Question

When you use fleqn and leqno and assign your own equations tags with \tag to equations in environments such as gather and align and you assign a tag with a certain length, then there's a line break after the tag. Given the same condition except that environment equation is used instead does not cause line breaks. How can I avoid the line breaks in the former case?

\documentclass[fleqn,leqno]{article}

\usepackage{amsmath}

\begin{document}

\begin{gather}
  \tag{one}
  1+1=2 \\
  \tag{two}
  2+2=4
\end{gather}

\begin{equation}
  \tag{three}
  1+1=2
\end{equation}

\end{document}

Answer 1

You can increase \mathindent, but I don't know why you want to use fleqn and leqno simultaneously:

\documentclass[fleqn,leqno]{article}

\usepackage{amsmath}
\setlength\mathindent{2cm}
\begin{document}

\begin{gather}
  \tag{one}
  1+1=2 \\
  \tag{two}
  2+2=4
\end{gather}

\begin{equation}
  \tag{three}
  1+1=2
\end{equation}

\end{document}