Inconsistent skimmer/water interaction in Jahai

[MorganOneNine.1025]

When mounted on a skimmer, the river around Yatendi counts as water (the skimmer moves faster) but the Rihlon River does not count as water (the skimmer moves slower, like on land).

Although the Rihlon is fairly shallow, that's never seemed to matter in other areas of Tyria so I don't think that's the issue. The only difference I see between the Yatendi water and the Rihlon is that the Rihlon water has a 'moving' texture--is that somehow messing with the skimmer's ability?