Dutch dictionary - Double vowel character changes to single vowel character

It is not a "problem" but rather a hardcoded exception to standard hyphenation rules. You can see that if you look up what the automatic hyphenation would have done without the exception rule:

... which is blatantly wrong – words in Dutch do not break between two same vowels.

Interestingly, this option of having a custom hyphenation seems new to recent IDs. Here is how the same word is broken in an older version, using the same dictionary:

Which is correct, with slightly different rules applied. [Those rules are not set in stone and so different interpretations are possible. I guess the same goes for other languages as well.]

Assessing correct hyphenation is best left to native speakers of the language (and if they disagree, suppress hyphenating the word in question).