Possible bug in JobStoreSupport.acquireNextTriggers()?

[fgunbin]

Hello,
When acquireTriggersWithinLock = false (default) and when selecting 1 trigger, acquireNextTriggers() skips obtaining LOCK_TRIGGER_ACCESS.
Below in acquireNextTrigger() there's Set<JobKey> acquiredJobKeysForNoConcurrentExec which tries to prevent acquiring more than 1 trigger for a non-concurrent job.
My question is, given that we don't own a lock, what prevents several instances from acquiring several triggers for one job?
Or what am I missing?
TIA

[fgunbin]

ping?