Problem with parachute.

Good morning.
I'm experiencing in some cases a weird behaviour of my spacecraft when using parachutes reentering on Earth, in particular when using big chutes to slow down capsules or even SRBs.
If for example i deploy chutes at 5000 mts, after a bit, although de indication of vertical speed in -9 or 11 m/s, the altitude begin increasing. If i close the chutes it drops again...
i'm using Solar System B by Felixhdz