Avidemux editing MKV

[hilltop]

Being as I am a virtual newbie at editing MKV please forgive me if my plea for help seems daft to you experts.
I have all the episodes of TV Series 'Pride & Prejudice' (legally bought & paid for), and I want to remove the instructions and credits for all episodes but the first. Read all I could and loaded the second episode to experiment. Straight forward I thought, slide the bar at the bottom - find the start mark it with A slide the bar to where its to be cut and mark it with B. Problem is I can't move the bar it keeps jumping back to the start. What the hell am I doing wrong? I thought this would be easy!!! - Help please

[poisondeathray]

use avidemux 2.6
http://avidemux.razorbyte.com.au/

you can only cut on keyframes (not frame accurate) - i.e. navigate with the "<<" and ">>" buttons

if you need a frame accurate editor, try solveigmm video splitter (not free)