The drawing helped a lot. The problem is that your dim text has been adjusted and is no longer being controlled by the dimension properties. You can see in this video that mirrored text mirrors properly when the text hasn't been moved.

If you look at the properties of your dimension you can see these properties grayed out.

You can see in a new dimension these are not grayed.

The reason that you cant use the command on all of them is that it uses the properties to adjust those values and those properties are no longer valid with the dimensions with moved text. This is also why you can only do it one at at time. The command has to identify the current location of the text and use that information to know where to move the text which is unique to each dimension. It cannot know how far to move the dim text on a group because they are all in different locations. (as @cadffm mentioned)
All that said there is one half way work around that you can use when and only when all the dimension text are on the same X coordinates. You can select all the dims and use the calculator to move all the text. This of course only applies to dims that are on the same X coordinate.

CADnoob
