KaraTemplater: util.fbf doesn't align with line's start_time and end_time

[scrpr]

when calling fbf function in template line like this:

Comment: !util.fbf("preline",0,400,1,"fbf")!
Comment: !retime("line",400,-400)!
Comment: !util.fbf("postline",-400,0,1,"fbf")!

often results lines to overlap:

Dialogue: 0,0:00:00.94,0:00:01.02
Dialogue: 0,0:00:01.02,0:00:01.70
Dialogue: 0,0:00:01.69,0:00:01.77

or not connecting to each other:

Dialogue: 1,0:00:02.44,0:00:02.48
Dialogue: 1,0:00:02.50,0:00:03.32
Dialogue: 1,0:00:03.32,0:00:03.36

It is fine for normal circumstances, but when I want to import this result with sync from another file using Merge Scripts, this will cause flickering.

The first and last frame should be checked so that their start time/end time would match the original line's time.