When chaining multiple jobs by using the option "Trigger/call builds on other projects", expanding variables in field "Predefined parameters" does not work properly.

Example where the first variable gets not expanded in any of the forms below:

step_number=$TRIGGERED_BUILD_NUMBER_$LAST_TRIGGERED_JOB_NAME

---returns "$TRIGGERED_BUILD_NUMBER_correct_job_name"

step_number=${TRIGGERED_BUILD_NUMBER_${LAST_TRIGGERED_JOB_NAME}}

---returns "${TRIGGERED_BUILD_NUMBER_correct_job_name}"

step_number=${TRIGGERED_BUILD_NUMBER_$LAST_TRIGGERED_JOB_NAME}

---returns the same as the second one

It would be practical to provide the value for TRIGGERED_BUILD_NUMBER with implicit last project name, or add new variable like LAST_BUILD_NUMBER that would provide it.
Thanks.