As discussed on IRC, change the ARJUNA12140 warning from the current:

"
ARJUNA12140: Adding multiple last resources is disallowed. Current resource is com.arjuna.ats.internal.arjuna.abstractrecords.LastResourceRecord@xxxxx
"
To:

"
Enlisting multiple non-XA resources into transaction is not allowed. Tried to enlist resource %s when resource %s is already enlisted.
"

Instead of showing the LastResourceRecord, it would help reduce the time it takes to locate the root cause, if we showed the underlying resources in the warning message.