Base point parameters are buggy. You should never place the base point parameter anywhere other than at 0,0 within block editor, especially when you have any chained parameters within the block. There are several bugs that often happen when you do. I don't think that is the cause of the issue you describe, but it is simply bad practice. I just delete the base point in the video to prevent it from causing issues. If you want it to remain in that location then move the base point to 0,0 and adjust all the linework/parameters accordingly. Also instead of acting on the base point directly, add a chained point/move and have that move the base point. Any actions you want acting on the base point should move the chained point/move and *not* act directly on the base point.
Your primary issues are that your Total length parameter does not interact with the Length left window or the Length right window chained parameters (neither of the stretch actions stretch them) and you do not have the appropriate stretch actions associated with those chained parameters. Both of those two chained parameters need to be added to the stretch action with the 0.5 distance modifier and the Length window right needs to be added to the stretch with the distance modifier of 1. Next, the stretch for the Length left window is associated with the point at the exterior of the window which is not ever moved/stretched by any of the other parameters and so it does nothing. That stretch action needs to be associated with the internal point which is actually stretched. That is most easily accomplished by rotating the parameter 180° so the associated point is at the center of the window. The Length right window has a single stretch associated with the external point. That action is correct but the parameter needs another stretch action associated with the internal point also and also with a 0.5 distance modifier.
I would also mention that there are extra objects within the block that are not ever visible, presumably because it used to have a visibility parameter that was deleted and those items are vestigial. If this is a block you plan to actually put into use and not just a pared down example block, then those objects should be deleted.
I recorded a screencast to demonstrate those issues, but Autodesk's uploading/hosting is currently not working. When it is working again, I will post the screencast.
