Unless I'm just going crazy, whenever I drink tea outside it has a slight aftertaste that I never get when I drink it elsewhere.
Edit to add, it has more taste, if that makes sense. It has a more complex taste.
The smell/taste senses are very closely related and cross paths in the brain somewhat.
If you ever want to freak yourself out plug your nose while you eat some of your favorite foods and only exhale slowly while chewing. It'll taste all sorts of weird.
My guess is the smell outside is interfering with what your brain is used to from the smell inside while drinking tea.
When you go outside with tea, I believe you are more nose blind.
When I eat leftovers the day after, or go camping, food tastes better because I am nose blind to the flavors. My brain becomes alert to sudden flavors when I eat outside, and grows fatigued when I am cooking/preparing indoors.
Being Northern Irish, I was raised on tea and drink 8 to 10 cups a day. Can't say I've ever noticed this. Where it is imbibed has no influence on the taste of it.
As an American who wasn't ever raised on tea of any kind (and I don't like coffee) but is starting to really learn to love teas and tasanes (I'm open to suggestions, by the way!), I have to ask: how the hell do you manage to drink 8–10 cups per day without dying of dehydration? If I drink more than 3 cups a day I start to really feel dried out!
Caffeinated beverages don't dehydrate you. Yes, caffeine has a mild diruetic effect, but it's nowhere near enough to cancel out the water in the drink.
Raised on tea. Elixir of the gods. And the water in it is still water. I'm well hydrated.
For suggestions, a good standard daily tea is Yorkshire Tea Biscuit Brew (it has malt in the brew so tastes like Rich Tea biscuits), and good Northern Irish teas are Punjana and Nambarrie.
My best guess is something related to a difference temperature causing us to perceive taste a bit different. If you're drinking tea outdoors, it's probably colder outside than if you're drinking it indoors.