You don't say what release. But I just went through a project on 4.4 with the InfoPrint 21 and had to apply many PTF's to get things
working okay, and there are still issues for which PTFs are pending. As I understand it the issue is being caused by a new print engine in the product line that has resulted in numerous changes to the way the ISeries/400 drives the device.
Look at the following;
SF63950, MF25055, SP63920, SF63854, SF63844, SF55237, SF59895, SF63673, SF62773, MF23611, SF63673, SF62933
And others released since early October.