Yes, this looks like a repeatable bug: when exporting a block from a layout, the text object is not visible when you open the block file in Rhino. An audit of the block file indicates that the text is actually present as a normal (i.e. not hidden) object but it will take a McNeel developer to work out why it doesn’t shown up.
However, there is a workaround: if you use the block manager to export the block while you are in one of the model viewports instead of the layout, then the text will show up in the block file.
HTH
Jeremy