Can you please provide more details. Eg. screenshot, etc.

Sorry, it appears that the wrong values in that case were caused by an intermediate build of the warnings plugin v4.0 that lacked the Javadoc parser.
Though I see on another project that a wrong value is shown in the graph. See the attached screenshot. The values for builds #51 and #52 have been processed by warnings v3.28 and are correct but then #53 (using warnings v4.4) shows wrong value where it should have 457.

Hmm, seems that there is no result at all (0 warnings). Does the same image appear if you enlarge the graph? Or press CTRL-F5 to recreate the graph...

And finally: can you start another build just to see if the warnings count stays at zero in the graph...

It looks like it's greater than 0 (see screenshot of enlarged graph). CTRL-F5 doesn't have any effect (is that command anywhere documented?).
The build.xml file won't make you happy, the ant build uses more than 50 build.xml files in several different locations (actually the build is for https://github.com/projectwonder/wonder)

Sorry, I mean the build.xml file in Jenkins build folder of your project. There Jenkins serializes the build results. In that file I can check if the WarningsResult is correctly serialized.

Did you already start another build?

There is the build.xml file.
I did a new build for which I attached already a screenshot before (build #54) but that showed no change.

Ok, thanks. From the build.xml I see that there are 7 warnings for Java and 457 for JavaDoc.

Maybe the wrong result is used in the JavaDoc trend. Does the trend graph for Java warnings work?

The Java trend graph seems correct.
On another project I have 1 Java and 0 Javadoc warnings but both graphs show 1. So your assumption seems plausible.

Ok, I can reproduce the problem. Seems that always the first result is used...

Code changed in jenkins
User: Ulli Hafner
Path:
src/main/java/hudson/plugins/analysis/core/BuildHistory.java
http://jenkins-ci.org/commit/analysis-core-plugin/bc48fb59837664ebddab0ef7233cd42e8f6a4c9e
Log:
[FIXED JENKINS-13656] Pick correct results for baseline.

Integrated in plugins_analysis-core #10445
[FIXED JENKINS-13656] Pick correct results for baseline. (Revision bc48fb59837664ebddab0ef7233cd42e8f6a4c9e)

Result = SUCCESS
Ulli Hafner :
Files :

• src/main/java/hudson/plugins/analysis/core/BuildHistory.java

Integrated in Jenkins Analysis Plug-ins (Compile) #488
[FIXED JENKINS-13656] Pick correct results for baseline. (Revision bc48fb59837664ebddab0ef7233cd42e8f6a4c9e)

Result = SUCCESS

Code changed in jenkins
User: Ulli Hafner
Path:
src/main/java/hudson/plugins/analysis/core/BuildResult.java
http://jenkins-ci.org/commit/analysis-core-plugin/6a01bb768e88b9697652e8e006cb39d00967ebfc
Log:
[FIXED JENKINS-13656] Make build history creation overridable.

Code changed in jenkins
User: Ulli Hafner
Path:
pom.xml
src/main/java/hudson/plugins/warnings/WarningsResult.java
http://jenkins-ci.org/commit/warnings-plugin/7db20dda08df20c7ba829a4c1b0f3d462e307140
Log:
[FIXED JENKINS-13656] Use warnings history when restoring an instance of
WarningsResult.

Integrated in plugins_analysis-core #10446
[FIXED JENKINS-13656] Make build history creation overridable. (Revision 6a01bb768e88b9697652e8e006cb39d00967ebfc)

Result = SUCCESS
Ulli Hafner :
Files :

• src/main/java/hudson/plugins/analysis/core/BuildResult.java

Integrated in plugins_warnings #404
[FIXED JENKINS-13656] Use warnings history when restoring an instance of (Revision 7db20dda08df20c7ba829a4c1b0f3d462e307140)

Result = UNSTABLE
Ulli Hafner :
Files :

• pom.xml
• src/main/java/hudson/plugins/warnings/WarningsResult.java

Integrated in Jenkins Analysis Plug-ins (Compile) #492
[FIXED JENKINS-13656] Make build history creation overridable. (Revision 6a01bb768e88b9697652e8e006cb39d00967ebfc)

Result = SUCCESS