Replacement string does not display backslash and the following letter

[celdorwow]

Expected behavior:
\begin{tabularx}{\linewidth}{cc}
X & X \\
\end{tabularx}

Actual behavior:
\begin{tabularx}{inewidth}{cc}
X & X \\
\end{tabularx}

Steps to reproduce

1. Create a snippet

snippet tabu "Regular tabular" b
\\begin{tabular$1}${1/(\*)$|(x)$/(?1:{\\\linewidth})(?2:{\\\linewidth})/}{${2:cc}}
	$0X & X \\\\
\\end{tabular$1}
endsnippet

2. Write tabu in a LaTeX file and press <TAB>
3. The snippet displays \begin{tabular}{cc} and holds on position after r
4. Appending * or x inserts {inewidth} in the middle but it should insert \linewidth.

As a comment, it doesn't matter how many times I escape \ in front of linewidth in the snippet

${1/(\*)$|(x)$/(?1:{\\linewidth})(?2:{\\linewidth})/}

or

${1/(\*)$|(x)$/(?1:{\\\linewidth})(?2:{\\\linewidth})/}

or

${1/(\*)$|(x)$/(?1:{\\\\linewidth})(?2:{\\\\linewidth})/}

the effect is the same.

---

• Operating System: 20.04.5 LTS (Focal Fossa)
• Vim Version: NVIM v0.7.0, Build type: RelWithDebInfo, LuaJIT 2.1.0-beta3
• UltiSnips Version: version 3.2 (05-Nov-2019) (up to date via Vim-Plug)
• Python inside Vim:
  • :py import sys; print(sys.version): 3.8.10 (default, Jun 22 2022, 20:18:18) [GCC 9.4.0], and
  • :py3 import sys; print(sys.version): 3.8.10 (default, Jun 22 2022, 20:18:18) [GCC 9.4.0]
• Docker repo/vimrc:

[celdorwow]

I solved it using a Python interpolation:

snippet tabu "Regular tabular" b
\\begin{tabular$1}`!p if t[1] == "x" or t[1] == "*": snip.rv=r"{\linewidth}"`{${2:cc}}
	$0X & X \\\\
\\end{tabular$1}
endsnippet

However, I am going to leave it open because I don't know if what happens with the transformation above is a bug or intended.