I reproduced and fixed the bug for the "Force column width" setting in Project Description column and Build Description column.
Can't reproduce it with the "Trim description" setting though.
Are you sure this doesn't work?

OK, it appears the "Trim description" checkbox setting is being retained correctly. I must have mis-observed that.

However, the "Force column width" entered doesn't seem to work exactly. For example I set it to 300 and I get something ~325 pixels in width. If I select 350 it uses ~400 pixels.

There is some additional padding, so it might not be pixel perfect.
I can't reproduce such big difference though.

Which browser are you using? Can you attach a screenshot?

Code changed in jenkins
User: Fred G
Path:
src/main/java/jenkins/plugins/extracolumns/BuildDescriptionColumn.java
src/main/java/jenkins/plugins/extracolumns/BuildDurationColumn.java
src/main/java/jenkins/plugins/extracolumns/DescriptionColumn.java
src/main/resources/jenkins/plugins/extracolumns/BuildDescriptionColumn/config.jelly
src/main/resources/jenkins/plugins/extracolumns/DescriptionColumn/config.jelly
http://jenkins-ci.org/commit/extra-columns-plugin/17388893c69bee63f1002f6ba7550d922dbec06e
Log:
JENKINS-21295 - Project Description column configs for trim and width
not correctly redisplaying

> Which browser are you using?

Latest Firefox.

Is this issue still relevant? Or can it be closed?

I'm no longer in a position to verify the relevancy.

Please re-open if necessary.