Weird repeated measure formatting

[Sebastiano Vigna]

Dear developers,
in the following test:

\version "2.4.3"

#(set-global-staff-size 18)

mainpattern = \drummode { bd8. sn16 r8 bd bd4 sn }

\score {
\new DrumStaff <<
       \context DrumVoice = "1" { s1*4 }
       \context DrumVoice = "2" { s1*4 }
       \drummode {
       <<
       { \repeat unfold 4 { hh8[ hh] } } \\
       \repeat percent 4 \mainpattern
       >>
       }
>>
     \layout {
       indent = 0\mm
     }
}


the repeated measures are formatted in a very irregular way: the first
two are almost as large as the non-repeated measure, the last is very
small.

-- 
Ciao,

                                        seba