I'm not quite sure how you're suggesting that the example shown should sound, but it definitely isn't ambiguous. The example given is no more ambiguous than a triple grouping with one quaver followed by a crotchet, or a crotchet followed by a quaver. A triplet quaver is half the duration of a triplet crotchet, so the notes under the bracket still last exactly two duplet crotchet beats. There is absolutely no ambiguity about how it should be read, the quavers are triplet quavers, not duplet quavers.
I am definately not saying the're duplet quavers, so here is my thought process;
It has the letter C at the start which to me is 4/4 time sig.
So my bar must add to four beats to conform to this time sig.
The first two crotchets are fine and uses two beats and take me up to the 4 notes under the triplet which will be played as one beat.
But now i am a beat short to resolve my commitment to the 4/4 time sig.
So i would play the first 3 notes as crotchets which is 3 beats and play the last three under the triplet as one beat thus i have played four beats in the bar which resolves my time sig. and commitment to the triplet.
Thinking about it in duplets take me to compound time sigs which 4/4 is not, and something i would not consider as option because the C has indicated to me a 4/4 time sig. which is a simple time sig.
So for me i have four notes, two of which are of a different value. For me a triplet is a group of three notes or rests played in the time of two notes or rests of equal value. which i don't have under this triplet. So as i stated, i would ask what is being said in the piece at that point.
So where have i misunderstood this one bar or have i just not explained myself well?
The OPs question was answered as far as standard triplets were concerend earlier in the post this is an extention from it.