Short description of error
The "Auto Texture Space" option in the "Texture Space" panel on the "Object data" tab is used to automatically calculate the texture space coordinates (which can be viewed by checking "Texture Space" in the "Display" panel in the Object properties ).
This option works well for Mesh objects. Adapting the texture space to the object's boundbox whenever it changes.
But with objects of type Text, the "Auto Texture Space" does not work. (For the boundbox can not be calculated through the objetct data.)
However the Cycles makes it seem like work. And the result shown in the preview of the cycles is not consistent with the actual size of the texture space of Text objects.
Exact steps for others to reproduce the error
This file shows the actual size of the texture space (in solid view) and the size that the cycles considered to be the auto texture space (render preview)
To check it out as it should be. Just see how this works on Eevee.