Custom workspace in matrix projects should be able to use axis as variables.

changelog.html

@@ -55,6 +55,8 @@ Upcoming changes</a>
 <!-- Record your changes in the trunk here. -->
 <div id="trunk" style="display:none"><!--=TRUNK-BEGIN=-->
 <ul class=image>
+  <li class=bug>
+    Custom workspace in matrix projects should be able to use axis as variables.
   <li class=bug>
     Fixed a problem in the concurrent matrix build.
     (<a href="https://issues.jenkins-ci.org/browse/JENKINS-13972">issue 13972</a>)

core/src/main/java/hudson/matrix/MatrixRun.java

@@ -176,6 +176,7 @@ public class MatrixRun extends Build<MatrixConfiguration,MatrixRun> {
             env.put("COMBINATION",getParent().getCombination().toString('/','/'));  // e.g., "axis1/a/axis2/b"
             env.put("SHORT_COMBINATION",getParent().getDigestName());               // e.g., "0fbcab35"
             env.put("PARENT_WORKSPACE",baseDir.getRemote());
+            env.putAll(getBuildVariables());
 
             // child workspace need no individual locks, whether or not we use custom workspace
             String childWs = mp.getChildCustomWorkspace();