Strange 1H-NMR signals/signal ratio
The paper specifically addresses this issue and ascribes it to the tendency for boronic acids to exist as solvent and concentration dependent oligomers:


  The dependence of the intensity ratio for these signals and the
  chemical shifts in the 1H NMR spectra on the concentration of the
  samples under study as well as on the nature of the solvents used
  indicates that anhydrides of boronic acids with different degrees of
  oligomerization can exist along with monomeric forms of these
  derivatives (ArB(OH)2) in solutions of substituted arylboronic acids.
  The conclusions about the existence of oligomeric forms of boronic
  acids and the absence of byproducts in the compounds isolated are
  supported by the results published earlier.


This type of equilibrium can be expressed like:


Higher order oligomers are also possible.