Don't know if you can consider it a bug. Merging is merging, 2 seperate topics become one. The only difference in merging topic A to B or B to A is the one that might get "This topic has merged" topic.

In flatmode, the normal vieworder is chronologically, so I think it works as designed.

What could be doable is an extra option called "Append topics", where a topic is appended to the target topic.

In normal day life, this isn't so much of a bother to use. We mainly use merge when somebody opens a new topic when there is already an older one about the same subject. You just merge them, and no troubles there (well, except bug #1 in this topic).

[Linked Image from siemons.org]