They do feel a little inconsistent, yes. Sometimes I am absolutely sure I did the movement correctly, and it just won't do a roll. Can't say 100% sure that it's not due to lazy input.

Here's another very strange bug I have:

Game region version: EU
Firmware version: 2.42
Console version and harddrive size: 80GB newest model
Custom soundtrack: yes
Controller type: DS3
Options settings: Motion control pitch only
Track [if any] where error occurs: all
Online/Offline: online only

As soon as I sign in to the online servers, the word PRESS appears at the upper right corner of my screen. I reduced the screen size in the options to see if there was anything else, and there indeed was: PRESS SELECT TO... (rest was offscreen). When I pressed select, something resembling a debug menu appeared, then the PS3 froze. I got pretty scared and did a hard reset. Now it appears everytime I log onto online, it even stays there during a race (layering right on top of the position display of the HUD). Needless to say I don't dare pressing select anymore...