Inconsistent Merge experience

When merging tickets, the experience is very inconsistent. Sometimes, it shows me the current requester's other tickets. Sometimes, it shows me the last ticket i worked on(probably because i'm multitasking and went away from Zendesk for a few minutes). 

Why not always show me this requester's other tickets? Why the delay on the tickets i've recently accessed(is this similar to the search API delay)?