Time units not saved if note is not mandatory

[basher]

OTRS version: 3.3.3

I wanted not to have a note sent to the owner when time units are filled in in the "Close" window.
I applied the following configuration:
1) in Ticket -> Frontend::Agent => I set "Ticket::Frontend::NeedAccountedTime" to "Yes"
2) in Ticket -> Frontend::Agent::Ticket::ViewClose => I set "Ticket::Frontend::AgentTicketClose###NoteMandatory" to "No"
3) unchecked " Ticket::Frontend::AgentTicketClose###Subject"

With this configuration "Time units" is a mandatory field. This is what I wanted.
But since a note is not entered (I set it as optional) then "Time units" I specified will not be saved.

This is clearly a bug of the system. I don't see why a note must be filled in to have "Time units" value saved.

Am I doing wrong? Any hint to reach my goal without modifying the source code?

[jojo]

first of all your system is outdated. actual version is 3.3.8

Actual design needs a note for the time units as they are bound to an article

[basher]

Thank you very much. This clarifies why my configuration did not work as I expected.
Anyway, considering that a note is mandatory in order to save time units Development Team should disable the possibility, as I did in my test, to set a "note" as optional and time units as mandatory.

This leads to confusion.