[racket] weird build failed after changing one character in docs that shouldn't affect anything

I was trying to make docs for ~>% and ~>_ in my fork of rackjure, and the travis cl builds were passing,
but then I changed one character in the documentation to fix a typo and then all of a sudden the build failed.
All I did was change one % to an _ within a @racketblock so this:
@racketblock[
(~>% #”foobar” bytes-length (number->string _ 16) string->bytes/utf-8)
]}
to this:
@racketblock[
(~>_ #”foobar” bytes-length (number->string _ 16) string->bytes/utf-8)
]}
And then all of a sudden the build failed.  
Is there anything scribble or anything else does that would make this not work?

https://github.com/greghendershott/rackjure/pull/42
https://github.com/AlexKnauth/rackjure/commit/39473e967a186d9a1d53aede461ba95d5bef16ac