Plugin update via manual upload seems to have a problem relating to jpi/hpi files.

Initially, our $JENKINS_HOME/plugins/ folder had the following contents:

• myplugin.hpi - old version
• myplugin/ - old version

Then I uploaded a new version of myplugin.hpi file via web upload function on the pluginManager/advanced page,
and restarted Jenkins.

1). On Jenkins 1.424.6, the update succeeded. The plugins/ folder was updated as follows:

• myplugin.hpi - new version (shown version name - OK)
• myplugin/ - new version - OK
• (myplugin.bak file was not created)

2). On Jenkins 1.447.1, the new version name was correctly shown in the plugin list,
but the update itself failed:

• myplugin.jpi - new version (shown version name - OK)
• myplugin.hpi - old version
• myplugin/ - old version - NG

3). On Jenkins 1.465, the update itself succeeded, but the old version name was shown:

• myplugin.jpi - new version
• myplugin.hpi - old version (shown version name - NG)
• myplugin/ - new version - OK

In the cases of 2) and 3),
when I removed myplugin.hpi and restarted Jenkins,
then both of the update and shown version name became O.K.