The map is a convert from a RTCW map and that might explain why it contains the file scripts/breakout.shader. However 2Bit also used the same filename for his shader in Breakout_371 (and earlier versions). Consequently breakout_et_b2.pk3 and breakout_371.pk3 should not both be in \etmain at the same time unless you like playing 2Bits map with it looking like he never finished shading it. However merging the 2 shaders seems to create a workaround.
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The shader
z_breakout_fix1.zip workaround is now tested and available on my filefront
page.