Analysis fails in numeric format with + sign

[jotabe-net]

Example:
This template is accepted by the analyzer:
"{Balance,10:#0.00}"
This isn't:
"{Balance,10:+#0.00;-#0.00;0.00}"
The problem is that the + in the format, is triggering:
Serilog002: Error while parsing MessageTemplate: Found invalid charater '+' in property

I don't know if the problem is that the '+' is not accepted in the whole property placeholder, or that this character is rejected in the format part