Mustache template doesn't allow [{{var}}] but template doesn't show warning

When using the template step using the Mustache format I set this format: "<id>: todo is complt id [{{id}}] #id" (Exported integration todo-test-export.zip )
And the resulting logs are "<2>: bbbbbbbbb is 0 2 ] #2" meaning for some reason the [2 got consumed somewhere and only ] made it into the log.
I haven't found the '[]' characters to have any meaning in the mustache syntax... apart from array indexing of the variables.