Tags with accents disappearing

It's been two months since I noticed that some of my tags kept disappearing from my tags list. I found that I could make them come back by just changing the folder name (I use folders with brackets to create my tags). At first I thought the tags that were disappearing were random, but recently I concluded that they were always the same and what they have in common is that they are all graphic accentuated words (words with graphic marks such as á ó ê): [Diários de viagem], [Memórias em fotos] and [Séries]. I'm from Brazil so I always use a lot of graphic marks in words since I write in Portuguese. Has anyone experienced something like this and know how I can solve this problem?