Very unlikely. You have a wiring problem. Look for something wired
incorrectly, a short allowing one circuit to cross over onto another, etc..

Well I presume you mean the front sidelamp comes on when you brake (the
sidelamp is inside the headlamp).

Which sounds like the brake lamp power is interfering with the tail lamp
circuit; when you press the brake, the brake power is sent back through the
sidelamp circuits illuminating the front sidelamps and rear tail lamps.

If you fitted the wrong bulb or the right bulb incorrectly this could be caused.

IIRC the Vento uses dual filament bulbs: these contain the 5w tail lamp
filament and the 21w brake filament and are connected to two separate contacts
on the cap. These bulbs have offset pins so that they should only be fitted in
the lamp unit one way, but it is quite possible to force them in the wrong way
round. Alternatively, the bulb you fitted may be a single filament 21w bulb
with the single contact on the cap in contact with both tail and brake
contacts in the cluster.

The latter will certainly cause the symptoms you describe, whilst the former
*may* cause it depending on contact spacings etc.

Ensure that the bulb you fitted is the correct bulb (double filament) and that
it is inserted the right way: the pins on the side of the bayonet cap line up
better the correct way than they do the incorrect.

And you're lucky you don't have bulb sensors on the Vento. I've known Alfa
156s require new instrument clusters due to damage caused by misfitted tail
lamp bulbs, believe it or not.