As long as salts are in solution, they tend to separate as ions. Consider sodium chloride or potassium carbonate... they dissociate (wrong word?) like husbands and wives at a party, each wandering around within the group: Na+, K+, Cl- and CO3-. They meet one another, separate, and go on their merry ways.
But when something LEAVES solution (as a solid) it stops being separate ions... it's a compatible pair at a singles dance leaving for dinner together. Once they leave solution, they're not separate entities mingling, they're a pair on their own.
OK, analogies are bogus, but that's the basic idea: they're only intermixing ions while dissolved in solution.