FreeGameDev

Probably many noticed it already but the shadows often appear to be “blocky”. I hope you know what I mean. This effect can be sometimes extreme when you’re moving at certain points on the track.

Is it possible to get rid of this somehow?

Well, no, from what I understood it's not.
It's actually a question for Ogre forum, since this happens in PSSMShadowCameraSetup code that aligns camera for shadow camera view.
But I'm sure it's a difficult thing and if it was possible it would be done already.