potassium oxalate in solution consists of potassium ions and oxalate ions. The oxalate will combine with any calcium ions to form insoluble calcium oxalate monohydrate.
There's no "stripping" going on - that's already done when you make the solution.
You won't manage to dissolve it, the only cure is prevention: Add a little potassium oxalate to the water, let stand for a day, then filter before use. Or use distilled / deionised water.