"No tremolo to end"

[Daniel Rosen]

I'm working on an extremely large project, and I've come across an error that I 
can't reproduce in a minimal example, so I'll try to describe it as best I can. 
When I compile a file containing this code,

    \version "2.17.97"
    one = \relative c''' {
      \time 3/8
      \key f \minor
      \repeat tremolo 3 { d16\ff( cis) } |
      \repeat unfold 11 { \repeat tremolo 3 { d16( cis) } | }
    }
    
    two = \relative c'' {
      \repeat tremolo 3 { f16\ff( g) } |
      \repeat unfold 11 { \repeat tremolo 3 { f16( g) } | }
    }
    
    \partcombine \one \two

the output appears as it should, but I get this error.

    warning: No tremolo to end
        \repeat unfold 11 { 
                            \repeat tremolo 3 { f16( g) } | }

If I change both "unfold"s to "percent"s, the excerpt compiles error-free.

Does anyone have any ideas about what could be causing this?

DR