Yes it does make sense. There are only 2 things I can’t think of that might be the case.
First is if the caps lock key is on (press it a couple times and fiddle). If it is, the video moniter will only update after you release the mouse from the slider. This option is useful if you have a low end pc and are working with really intensive effects… otherwise the system would keep freezing and going reeeeeeaaallly slooowwww.
The second option could be if you have the opengl static textures mode selected for previewing your video. In the video moniter there is a button called ‘fast previews’. When clicked it brings up a drop down box with a bunch of options. I have mine set to ‘adaptive resolution’, but you might have yours set to ‘opengl static textures’. At least the same symptoms happen for me when I’m in that mode.
Hope I could help.
peace,
Michael