GTA San Andreas - Problem with unique jumps

[sit5]

Hi homies!
I've almost finished the game, I'm at 95,79%. I've to make all the unique jumps except four that I made during some mission in Los Santos.
I also have to make the Vigilante Missions and the Races in LV airport.
I tried to make the first two jumps in LS. I started with the one in El Corona and the one in Willow Field. In both cases I've seen the jump in slow motion, but no messages and no rewards!!!
I tried to do again and again the jumps but the result was always the same!!!
I tried to use some other vehicles (bikes, Valentino's bike, fast cars like Infernus, Super GT, etc....) but nothing was change!
I've even tried to make them in the other sense...
So I decided to try with other jumps... The outcome was exactly the same!!!
DAMN JUMPS!!! They're realy trying my patience!!!
What's the problem? Does anyone had the same problem and found a solution?! Does someone knows the reason, if there's one...???
Thanks to all the homies!!!