Maxim Cournoyer <maxim.cournoyer@gmail.com> writes:

> Hi,

Hi Maxim,

> Would someone be able to explain what is responsible for this?  It seems
> to me it'd be preferable if the subject of the message I'm replying to
> was kept rather than replaced this way, to preserve context.

FTR, this behavior is due to setting a default subject via
gnus-posting-styles in debbugs-gnu-summary-mode. Could you please check
whether the appended patch helps?

Best regards, Michael.