in ProbTrackXBaseInputSpec the random_seed input is set as a boolean, instead it should be a number used to initialise the random number generator and it's useful in the setting of splitting tractography over multiple threads (https://www.jiscmail.ac.uk/cgi-bin/wa-jisc.exe?A2=ind1603&L=FSL&D=0&P=34677)

So i think that in ProbTrackXBaseInputSpec should be something like this:

random_seed = traits.Int(argstr="--rseed=%s", desc="a number to initialize the random number generator")