I found an issue, probably related to encoding. The dutch word "ideeŽn" (ideas) is underlined with the dutch spelling. The suggestion is to transform it to: "idee√ęn". This is of course incorrect. So, it looks like it can't handle special characters too well... I also checked with other words with accents.
If I put the word in the custom dictionary, it is counted as correct. However, it looks like the words in the custom dictionary are not considered as alternative spellings.