It is not the first time it happens:
galaxyproject/iwc#276
While there is no error in the autoupdate itself, there is a bug in the report:

toolshed.g2.bx.psu.edu/repos/devteam/picard/picard_MarkDuplicates/2.18.2.4 should be updated to toolshed.g2.bx.psu.edu/repos/devteam/picard/picard_MarkDuplicatesWithMateCigar/2.18.2.3