It could be to check whether there are some large shareholders who still wants to get out, i.e check whether the PPS will continue to go down.
However, 400k shares isn't more than 0.16MUSD, so it's only big for retail - big(ish) players might want to get as many shares as possible while the dilution continues and before the Q2-report. If they have paid attention to the CC as well, then they should expect the PPS to jump a bit sometime during June (when the info about the AFs are released) - normally temporary, but if the dumping stops/slows then it might not be.