Tempo sliding over key signature changes

[address@hidden]

Hey all,

My minimal example below functions quite nicely w/ the placement of tempos but 
my example from a score (see attached image) has the tempo sliding over the key 
signature changes.  Does anyone have intuition about where this discrepancy 
could come from?

\new Staff << {
  \time 7/8
  s1*7/8
  \tempo 2=88
  s1*7/8 |
  \time 3/4
  \tempo 4=148
  s2. |
  \tempo 4=116
  s2. |
}
{
  \key b \major
  b2 b4.
  \key bes \major
  b2 b4.
  \key e \major
  b2.
  \key ees \major
  b2.
} >>

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