The link to JavaDeployReg.log from customers:
https://bugs.openjdk.java.net/secure/attachment/24867/JavaDeployReg07.log
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jp2ssv dll missing in D:\jdktest\bin
ssv dll missing in D:\jdktest\bin
SSVSetup FAIL
Register for elevation
update elevation policy for ssvagent OK
update elevation policy for jp2launcher OK
tell IE to refresh elevation policies after undate registry OK
RegisterforElevation OK
  isFileExist for [D:\jdktest\bin\dtplugin\npDeployJava1.dll] return FALSE (error code 5)
...

For some reason some dlls(jp2ssv.dll, ssv.dll, dtplugin\npdeployJava1.dll) are not copied to JAVA_HOME/bin before the moment when RegisterDeployEx() is called by the installer.
According to the provided log, the user reproduced it on 8u25, specified install directory as "D:\jdktest". I've tried to do the same, but on my system it works without any errors, the dlls are copied as expected(before RegisterDeployEx() is called by the installer).
In the deployment code, we just use _tstat() to check that file exists, and that code hasn't been modified for several years, so there should not be problems from deployment side. I think this needs to be investigated on installer side(at least to determine if there are cases when those dlls are not copied properly).
This issue can be related with JDK-8049056
 "Deployment .jar files are missing in JAVA_HOME\lib, when installer calls RegisterDeployEx() from deploy.dll"