I've create multijob project which comprises of 4 phases. Phase 1 has 2 jobs to run in parallel and phase 2 also has 2 jobs to run in parallel. Phase 3 has 3 jobs to run in parallel . Phase 4 has 1 job to run parallel. Phase 1 to 4 are sequential.
Now when i execute the multijob project. 1st job in the phase 1 gets executed along with 2nd job in phase 2. When the 1st job gets executed, it runs on several nodes ( 20 nodes). But multijob marks this job is complete only taking the 1st node output and doesn't wait till the remaining 19 nodes to complete the job.

Screenshot attached contains the full details.

Here is the console output :

Started by user anonymous
[EnvInject] - Loading node environment variables.
Building remotely on den00rfu- FA Component MATS Box (FA INTEG) in workspace /scratch/fusion_apps/workspace/Risk1_REL9_103600FABP_PSU_Single_click
>> Job status: [Machine_Setup_INFRA_SC] the 'build only if scm changes' feature is disabled.
Starting build job Machine_Setup_INFRA_SC.
>> Job status: [REL9_DB_LDAP_HEALTHCHK] the 'build only if scm changes' feature is disabled.
Starting build job REL9_DB_LDAP_HEALTHCHK.
Finished Build : master of Job : REL9_DB_LDAP_HEALTHCHK with status : SUCCESS
Finished Build : adc2121117 of Job : Machine_Setup_INFRA_SC with status : SUCCESS
>> Job status: [ARU_SFTP_PATCH_DOWNLOAD_1036FABP_US_KITSITE_Parameterized_SC] the 'build only if scm changes' feature is disabled.
Starting build job ARU_SFTP_PATCH_DOWNLOAD_1036FABP_US_KITSITE_Parameterized_SC.
>> Job status: [P4EDIT_INSTALL_ACTIVELOAD_JOB_SC] the 'build only if scm changes' feature is disabled.
Starting build job P4EDIT_INSTALL_ACTIVELOAD_JOB_SC.
Finished Build : #8 of Job : ARU_SFTP_PATCH_DOWNLOAD_1036FABP_US_KITSITE_Parameterized_SC with status : SUCCESS
Finished Build : #8 of Job : P4EDIT_INSTALL_ACTIVELOAD_JOB_SC with status : SUCCESS
>> Job status: [REL9_BUILD_LINUX_SCRATCH_SC] the 'build only if scm changes' feature is disabled.
Starting build job REL9_BUILD_LINUX_SCRATCH_SC.
>> Job status: [REL9MAN_BUILD_LINUX_SCRATCH_SC] the 'build only if scm changes' feature is disabled.
Starting build job REL9MAN_BUILD_LINUX_SCRATCH_SC.
>> Job status: [REL9_GETACTIVECONF_CN] the 'build only if scm changes' feature is disabled.
Starting build job REL9_GETACTIVECONF_CN.
Finished Build : #128 of Job : REL9_GETACTIVECONF_CN with status : SUCCESS
Finished Build : adc6160113 of Job : REL9MAN_BUILD_LINUX_SCRATCH_SC with status : SUCCESS
Finished Build : adc2121117 of Job : REL9_BUILD_LINUX_SCRATCH_SC with status : SUCCESS
>> Job status: [REL9_THIRDEYE_DQA] the 'build only if scm changes' feature is disabled.
Starting build job REL9_THIRDEYE_DQA.
Finished Build : master of Job : REL9_THIRDEYE_DQA with status : SUCCESS
Warning: you have no plugins providing access control for builds, so falling back to legacy behavior of permitting any downstream builds to be triggered
Finished: SUCCESS

So it says
Finished Build : adc2121117 of Job : Machine_Setup_INFRA_SC with status : SUCCESS
adc2121117 being the first node in Machine_Setup_INFRA_SC , multijob marks the status success after finishing the build. But doesn't wait for other nodes to complete the build which follows after adc2121117.