Let K be a function field of characteristic p > 0. We recently established the analogue of a theorem of Ku. Nishioka for linear Mahler systems defined over K(z). This paper is dedicated to proving the following refinement of this theorem. Let f 1 (z), . . . fn(z) be d-Mahler functions such that K(z) (f 1 (z), . . . , fn(z)) is a regular extension over K(z). Then, every homogeneous algebraic relation over K between their values at a regular algebraic point arises as the specialization of a homogeneous algebraic relation over K(z) between these functions themselves.If K is replaced by a number field, this result is due to B. Adamczewski and C. Faverjon, as a consequence of a theorem of P. Philippon. The main difference is that in characteristic zero, every d-Mahler extension is regular, whereas, in characteristic p, non-regular d-Mahler extensions do exist. Furthermore, we prove that the regularity of the field extension K(z) (f 1 (z), . . . , fn(z)) is also necessary for our refinement to hold. Besides, we show that, when p d, d-Mahler extensions over K(z) are always regular. Finally, we describe some consequences of our main result concerning the transcendence of values of d-Mahler functions at algebraic points. arXiv:1808.00719v1 [math.NT] 2 Aug 2018 1. E is separable over k. That is, there exists a transcendence basis F of E over k such that E is a separable algebraic extension of k(F ) (see [9, Appendix A1.2] and also [17]).2. Every element of E that is algebraic over k belongs to k.