PROCEDURE TO REPRODUCE:
On a staff with current clef as bass clef, in 4/4 time,
insert a D# half note (below middle C). Change the
clef on the 3rd beat of the same measure to tenor clef.
Insert an A (natural) half note on the 3rd beat - it
will be on the same line as the D#.
Since the A occurs on the same line as the D#,
rosegarden adds a natural sign to the A (apparently, to
override the sharp sign for the D#). However, this
natural sign is not necessary: Anyone reading the staff
will see the change from bass to tenor clef and will
realize, whether or not the A is preceded by a natural
sign, that the new note is an A natural, not an A
sharp, since the clef change is obvious - the new clef
is very easy to see.
The natural sign actually gets in the way and could
slow a person down who is reading (or performing off
of) the part - it is extra, unneeded information that
could confuse the reader.
I tried a similar procedure switching from alto to
treble clef and saw the same result. I suspect this
effect will occur whenever this same pattern occurs
with any clef change.