Logback colorisers add random whitespace in 2.4, but not in maven

Console logback logs when colorised with fr.norad.logback.prettier or org.tuxdude.logback.extensions in standard configuration add random whitespaces to output (non-colorised logs are ok):

09:59:50.536 [main      ] DEBUG    u.a.s...
09:59:50.537             [main      ] DEBUG    u.a.s...
09:59:50.540 [main      ] DEBUG    u.              a.s...
           09:59:50.541 [main      ] DEBUG

Doesn’t happen to the same (very basic) java app project when run in maven. Both slf4j-log4j12 and log4j are excluded from other dependencies. Gradle 2.4, Java 7, OS X 10.10.3, Maven 3.1.1