Exactly. So while thrown, it follows the rules for ranged weapons... which means you can't use it as a melee weapon when you throw it.
-Hyp.
A one-handed weapon, by your -own- interpretation is a one-handed weapon regardless if it is versatile and is used as a two-handed weapon.
Why is this? Because it is under an entry as a one-handed weapon, regardless of whether you use it in two hands. This is the logic that applies.
The -exact- same logic applies when throwing a melee weapon with the 'heavy thrown' trait. At no point does it -stop- being a melee one-handed or melee two-handed weapon. The thrown ability means you use it as an -exception- to the rule. It does not change the weapon's properties one bit.
If a versatile weapon stays a one-handed weapon when you use it two-handed, a melee weapon stays a melee weapon when you use it in a ranged attack.
If the power were only limited to melee basic attack, it would say 'melee basic attack.' It does not. It says 'basic attack with a melee weapon' which is a different thing. Nothing you can do with a javelin changes the fact that is, for all intents and purposes, a one-handed melee weapon that you can use as a ranged weapon because of a property it has. You can throw it, but its entry remains where it stands on the chart.
Here's the rub. You throw the weapon and 'it counts as a ranged weapon.' However, nothing -stops it- from having all the traits and properties of a melee weapon. It is still a melee weapon, but it also counts as a ranged weapon for that attack.
The assumption that the weapon cannot have both properties simultaneously is merely an assumption and is not explicitly nor implicitly backed by any text in the game.
Regardless, the logic is very simple. If using an object as something else does not explicitly make it stop being what it is, then it still is what it is. It's the one-handed versatile logic applied directly to this situation.