Variable incorrectly perisists in loop when I redefine a print method

[DarkClaw1]

I asked about this on the discourse and it was recommended I open an issue:
https://discourse.julialang.org/t/redefining-print-method-changes-variable-scoping-in-loop/108010

Essentially the idx_last variable persists when it should not.

using Printf
for n in 1:10
    if n == 1
        flag     = true
        idx_last = 1
    else
        flag     = true
        idx_last = ifelse(flag, n, idx_last)
    end
    Base.show(io::IO, f::Float64) = @printf(io, "%.2f", f)
end

If I comment out the Base.show() line then I correctly see UndefVarError: idx_last not defined.

This happened for me using versions 10.10.0-rc2 and 1.10.0. Apparently the expected behavior was seen using v1.9.4 on windows. Also, from the discourse you can see we verified idx_last is never in the global scope. My versioninfo:

Julia Version 1.10.0
Commit 3120989f39b (2023-12-25 18:01 UTC)
Build Info:
  Official https://julialang.org/ release
Platform Info:
  OS: Linux (x86_64-linux-gnu)
  CPU: 64 × AMD Ryzen Threadripper 2990WX 32-Core Processor
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-15.0.7 (ORCJIT, znver1)
  Threads: 1 on 64 virtual cores