Bear with me - - I'm new to Presta valves.

I was pumping the tires up last night, and noticed when I unclamp the nozzle from the valve, I can't
seem to quickly and carefully pry it off of the valve without the valve releasing a quick burst of air; just a quick 'broosh' - like the sound of an air gun. Is that an inherent 'thing' that just happens with Presta valves, or does my techinque need some tweaking? If it's inherent, do you over-inflate a little to compensate for anything that shoots out of there when removing the nozzle? Also - - there is a nut at the bottom of the valve that rests against the rim. I assume this nut is supposed to be pretty tight against the rim, correct? Yeah, Yeah, BEGINNAH from BAWSTIN!

I don't know if it's true but I was told that the air which goes "psht" is only the air pressure in the hose of the pump. I just hand tighten the screws on the valve to firmish.(is that a word???)
Steve.

You could overinflate a pound or two to make sure you are at the right pressure once you have released the pump. Afterall tire inflation is not a super precise part of the bike. I would guess the small pop and whoosh is mostly air from the hose, but its easy to compensate.

The nut should be snug enough to hold the valve in place, but it doesn't need to be more than finger tight for that purpose. Remember as you inflate the tube you'll pull the nut down tight against the rim. If you get it too tight its a PITA to loosen when you get a flat and have to pull the tube.

That's almost certainly air coming out of the pump hose, not the tire.

You're fine. Presta valve only allows air to flow into the tire, unless you press the tip with your finger. It is possible the pump head will knock the tip a bit as you pull it off and let some air out, but that is negligible. The whoosh is mainly from the pump and hose.

Cool! Thanks!

Lookie here

Doggus! Why! Why did you refer me to that disgusting thread!!??