Sorry to raise this again.
It has been suggested to me that when V6 cuts dimension text in half it is something to do with Windows updates and or the Intel graphics driver on my HP laptop.
I updated Rhino 6 yesterday and now all the text in a dimension disappears.
I have Rhino 5 on the same machine. I have tried cutting and pasting between V6 and V5. In V5 the dimension line shows correctly with its text, but in V6 the text disappears.
Notice this effect is the same if the original geometry is created in V5 or V6.
The laptop is the common, The operating system is common. The drivers are common. V5 is OK V6 is not.
It looks as if it is entirely down to a bug in the Rhino code.