Orange Tree Evolution Steel Str Gtr strumming problems

[Gone To Lunch]

In my Orange Tree Evolution Steel Str Gtr I am alternating between two strum patterns, one on C0, alternating every measure with one on C0#.

However every few bars the articulation of the first strum of the bar, on beat 1, changes to a palm mute instead of the sustain that is displayed in the graphic ? That is, it changes itself to a mute at the first strum, on beat 1, after the previous pattern ?