It is very rare, I don't know if it's Ipoker's fault or HM3.
Hand doesn't import, manual import returns error: "Warning: Big Blind not posted in hand#XXXXXX
After reviewing the xml files, I found following mistakes in two lines:
<action cards="" sum="€0.20" no="2" type="2" player=""/>
<action cards="" sum="€0" no="8" type="0" player=""/>
So, it sometimes leaves player nickname empty, then fails to import if that particular player is in the big blind.
Nothing to worry about because it's only a few hands, but I'm letting you know.