Short rainbow circuit conjecture for regular matroids

Let $M$ be a simple regular matroid, let $r(M)$ denote its rank, and let $c$ be an $(r(M)+1)$-colouring of $M$. A rainbow circuit is a circuit whose elements have pairwise distinct colours. It is short when

$$|C|\leq \left\lfloor \frac{r(M)+2}{2}\right\rfloor.$$

Short rainbow circuit conjecture. If $(M,c)$ has no colour-singular elements, then $M$ has a short rainbow circuit. This conjecture extends the corresponding rank-two case from graphs to regular matroids. The supplied text does not state whether it has been resolved.