That's a very old bug with the costume creator, it's not Mac related. The devs likely know it exists and haven't managed to fix it yet.
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I'm not sure if this is specific to the Mac version, and I've done a search to find any related posts, but came up empty.
Every time I go into the costume creator, the game changes my costume - sometimes a few pieces, sometimes the entire costume. This is before I've even attempted to make any modifications. A few times, I've gone and switched everything back (at the cost of a free token) and then when I've gone back into the game, a costume piece will have either been added or deleted (costing me another token to put it back or remove it). This has happened in every server I've tried. Logging out and restarting the game doesn't stop this from happening.
Has anyone else experienced this?
Thanks!