I'm encountering an issue similar to JENKINS-12514 with Jenkins 1.450.

Update manager reports that I'm running subversion plugin 1.34 and 1.37 is available. In my plugins folder I can see:

rw-rw-r-. 1 jenkins jenkins 2105983 Feb 2 15:20 subversion.bak
rw-rw-r-. 1 jenkins jenkins 2105983 Feb 2 15:20 subversion.jpi

I tell Jenkins to install 1.37. Once it's downloaded I can see:

rw-rw-r-. 1 jenkins jenkins 2105983 Feb 2 15:20 subversion.bak
rw-rw-r-. 1 jenkins jenkins 2103308 Feb 2 15:43 subversion.jpi

Checking the manifests:

[jenkins@XXXX plugins]$ unzip -p subversion.bak META-INF/MANIFEST.MF | grep Plugin-Version
Plugin-Version: 1.34
[jenkins@XXXX plugins]$ unzip -p subversion.jpi META-INF/MANIFEST.MF | grep Plugin-Version
Plugin-Version: 1.37

Restart jenkins to apply the changes. At this point, the present files are:

rw-rw-r-. 1 jenkins jenkins 2105983 Feb 2 15:20 subversion.bak
rw-rw-r-. 1 jenkins jenkins 2105983 Feb 2 15:20 subversion.jpi

and the manifests:

[jenkins@XXXX plugins]$ unzip -p subversion.bak META-INF/MANIFEST.MF | grep Plugin-Version
Plugin-Version: 1.34
[jenkins@XXXX plugins]$ unzip -p subversion.jpi META-INF/MANIFEST.MF | grep Plugin-Version
Plugin-Version: 1.34

And update manager still reports 1.34 with 1.37 available.