Windows 7 Professional 64-bit SP1
Nvidia GeForce GTX 760
Broken: Blender 2.75a ...up to and including current version... 2.77 rc2
Description: Under certain circumstances the numerical buttons in the Video Sequence Editor will refuse to accept value changes.
To produce this bug do as follows:
Open Blender to default scene of cube.
In camera properties/shading set alpha from ‘Sky’ to ‘Transparent’.
Go into VSE and add a movie strip.
Now add default scene strip on top of movie strip.
Set scene strip to ‘Alpha Over’.
With scene strip still selected go to frame sixty (60) on timeline. (exact frame not important)
In the Edit Strip section on the right of the channel window set a keyframe for Opacity.
Once this first keyframe has been set the value button will no longer want to accept changes to the numerical data. It does not matter whether one slides the numerical data with the mouse, or enters it by clicking and pressing the ‘enter’ key. The numerical data will always want to reset itself to the value of the first keyframe pressed.
Going to a different frame and attempting to enter other numerical data into the value button gives the same results. [ Workaround: The value button(s) will, however, still accept a new keyframe and the value of that keyframe can then be edited in the graph editor. ]
Once this odd behaviour has started, the same thing will occur with the other channels. In either the movie strip or the sound strip, values in the editing fields can be changed successfully until a first keyframe has been entered for some property. After that, the field will no longer want to change.
Please note: This example used the ‘Opacity’ value, but almost any animatable value button will trigger the same behaviour.
Also, it does not matter which strip one selects first (scene, sound or movie clip) the same thing will happen.