It could very well be that the issue is the data type. Not sure what DWIConvert does with float data (it probably casts it to short/Int16), as it expects short data. A possibility is that the nifti header says one thing and some FSL tag in the header says another thing (i.e. the data is actually not float, as the nifti header info is wrong).

Did you get the raw dwi data directly from the DICOM conversion? The acquired raw data should be in short, not float. Also pixdim4 should be 1 or 0 (the 4th dimension is the DWI volumes, in this case you have 33 DWIs, which have, according to fslinfo, a spacing of 8.8, which is really non-sensical as DWIs don't really have a spatial spacing), though i don't think that this is what causes DWIConvert to do something incorrect.

What conversion tool did you use (we use dcm2niix to go to nifti data from DICOM), maybe that's the issue? Alternatively you could go from DICOM to NRRD with DWIConvert, apply DTIPrep and then convert to Nifti for further processing in FSL. 

Martin