The reason for one of the changes is that the mvel pom.xml does not match the hierarchy in which it is found. This causes ivy to reject the configuration.
I thought I had fixed this issue but my changes actually broke the build. This was hidden from me/CI as we had already downloaded the appropriate metadata.
The real way to fix this is to change the mvel organisation to org.codehaus.mvel (reflecting the pom organisation) and include a module definition in the ivysettings which will override the normal path configuration of the m2 repository.
My bad, apologies to all.