Yes, because when you sell it, you get cash and profit. Profit is taxable, in Germany they tax it with 25% + Solidarity Tax + Church Tax (if you are a member of a church).
After, you can go ahead and buy another fund, but in between you "shed" a significant amount of money.
replyDetails depends on jurisdiction, of course.
replyIn the US, you would likely also have to pay capital gains taxes for such a trade. (I think.)
In Singapore, in contrast, swapping between funds like this would not have any tax implications.