Due to https://issues.jboss.org/browse/JBTM-1431, it is possible for a last resource (e.g. non-XA resource) to be committed prior to another XA resource, which is unsafe.
This was fixed in master prior to 6.1, but not in a bugfix release so was not pulled into EAP.
Fix backported to 4.17 branch by Tom, https://github.com/jbosstm/narayana/commit/986d7792d2dbcc5d01844a5f2240a31a1f5d78b2
Tom Jenkinson <tom.jenkinson> updated the status of jira JBTM-1431 to Closed
Went into 4.17.9
Verified on revision EAP 6.4.0.DR12.
Last resource is committed before XA resources.
For safety reasons the "Commit Markable Resource" is added in EAP 6.3.0. (http://documentation-devel.engineering.redhat.com/site/documentation/en-US/JBoss_Enterprise_Application_Platform/6.3/html-single/Development_Guide/index.html#sect-About_the_LRCO_Optimization_for_Single-phase_Commit_1PC)