The Cottage Smallholder

As I bought a load of fresh ginger last week (and the CSH site was down) I decided to have a go at preserved ginger. I found a recipe and all went well till the last bit. I bottled it and sealed it immediately (as I would do normally for jams & chutneys). A few hours later when I went to look at it, the sugar syrup seems to have crystalised. I can't understand why, I did everything as per the recipe - apart from the end bit, it said I sould leave it to cool before sealing. Is it possible I over boiled it and the sugar syrup was too 'strong' (evaporated off too much water) - however, I have to say, it tastes gorgeous.