imod It's not actually needed to change anything, just opening the configuration page and saving again, makes this happen.

This automated test reproduces the issue:

@Test
    public void sameFolderPropertyAfterConfiguration() throws Exception {
        Folder f1 = createFolder();
        ConfigFileStore store = getStore(f1);

        r.configRoundtrip(f1);

        assertThat(store, Matchers.is(getStore(f1)));
    }

I think it's related with AbstractFolder because the properties are not being sent in the json after configuring.

I am not sure of why though. Maybe they are "invisible" properties?

Code changed in jenkins
User: imod
Path:
src/test/java/org/jenkinsci/plugins/configfiles/folder/FolderConfigFileActionTest.java
http://jenkins-ci.org/commit/config-file-provider-plugin/679be2283e7bf812745d6278edcfdf5533a0b4d9
Log:
JENKINS-42389 add test case to demonstrate problem

egutierrez I also asked on the ML for some hints on how to resolve this issue - unfortunate with no luck  

...maybe you could ask around internally?

imod sure, let me try and will come back to you.

My suggestion on the list was to make FolderConfigFileProperty a ReconfigurableDescribable.

hmm, strange that never made to my mailbox  - thanks!

Code changed in jenkins
User: imod
Path:
src/main/java/org/jenkinsci/plugins/configfiles/folder/FolderConfigFileProperty.java
http://jenkins-ci.org/commit/config-file-provider-plugin/3a4282fe3ead6de1de1d3b8034646083f1dfc380
Log:
[FIXED JENKINS-42389] implement ReconfigurableDescribable to fix data lost when folder gets updated

Code changed in jenkins
User: imod
Path:
src/main/java/org/jenkinsci/plugins/configfiles/folder/FolderConfigFileProperty.java
src/test/java/org/jenkinsci/plugins/configfiles/folder/FolderConfigFileActionTest.java
http://jenkins-ci.org/commit/config-file-provider-plugin/f7206995991ee2cbbc2dca750aee2290609f994f
Log:
Merge branch 'JENKINS-42389'

Compare: https://github.com/jenkinsci/config-file-provider-plugin/compare/dbda7551cec1...f7206995991e