StringPairReplacer replacement woes

I’m using StringPairReplacer to replace some tags (inside $ chars) in a snippet code to their default value, which fails.
Since SPR doesn’t accept (dynamic) variables for replacement string, only parameters, I’ve enclosed it in a custom transformer, and using its parameters to transfer the value of the replacement string.
But it still fails with
“@Tcl2 -- failed to evaluate expression `Replace_replacement_tags_StringPairReplacer_2_fb7401f4_4759_4fdf_9add_13b9915a14686_replace' -- char map list unbalanced”
The replacement value is given below in blue, and it works if I insert it as a fixed string.
$schema$ dbo $table_name$ table_name $column_name$ column_name $data_type$ VARCHAR(20) $null$ NULL $collate$ Latin1_General_CI_AS $default$ NULL
Am I fighting some TCL or FME escaping, or could it be a bug in SPR ?
Fails in both 2020 and 2026.
Cheers.