Cannot reset TupletNumber back to visible

[Raphael Manfredi]

[Resent because I never received the message back]

I've been using

        \override TupletNumber #'transparent = ##t

in 2.8.6 to make the tuplet number disappear after measure 2 of a score
consisting mainly of triplets.  However, on occasions there are tremolos
for which I would like to display the triplet above, so I've tried to
encapsulate those thusly:

        \times 2/3 {
          \override TupletNumber #'transparent = ##f
          g:8 d:8
          \override TupletNumber #'transparent = ##t
        }

But this does not work.  Once the transparent has been set to true, it
seems to be sticky.

Is that the expected behaviour?  How can I restore tuplet numbering
temporarily?

Raphael