Patchy runs a merge attempt even when staging/master are both up to date

[James]

Hello,

i wondered why patchy bothers to run its merge script when staging and 
master are already in sync?

In this case there was simply an update from release/unstable -> 
origin/release/unstable.

See log:

--snip--
(UTC) Begin LilyPond compile, previous commit at 
5bff1f78f6cc4d3893e25abead15d928ca00c041
From ssh://git.sv.gnu.org/srv/git/lilypond
   07adeda..3ed0fd8  release/unstable -> origin/release/unstable
Merged staging, now at:    5bff1f78f6cc4d3893e25abead15d928ca00c041
    Success:        ./autogen.sh --noconfigure
etc.

--snip--

What happens here is that the merge 'checks' all complete and then I get 
the 'this has already been pushed by another revision' message.


Not that it matters to me for merging but it means that anyone else 
(including me) who now runs a test-patchy for a new patch has to rebuild 
their test-baseline for the check, even though 'nothing' in staging or 
master has changed.

James