Metathesis only occurs across of morpheme boundary.

Editor's note: Metathesis in this case may have been a perceptually motivated process. That is, the sequence resulting from metathesis is better perceptually than the input sequence. The reason for this is that liquids have more robust internal cues than obstruents due to clear formant structure throughout the duration of the liquid which provides strong cues to both place and manner of articulation. On the other hand, by having no formant structure at all, stops have less internal cues to both place and manner than liquids. Therefore, shifting a stop to the prevocalic position, at the expense of the liquid with stronger internal cues, can be understood as strengthening the perceptibility of the stop. Similarly, a laryngeal stop lacks strong place cues (given that it has no supraglottal contriction). Positioning it in prevocalic position may also make it easier to identify (for related discussion, see Hume 2001, Mielke 2002).