Something similar happened in Argentina. +60% interest rates with 45% "official" inflation and a constant exchange rate with the USD. I was able to get returns of more then 60% in USD because I sold my mutual funds and bought dollars before they chose to devaluate the peso.

The problem was they allowed the currency to devaluate in a matter of days. People with CDs or mutual funds with long withdrawal time lost a lot of money. I'm talking about going from 18pesos = 1 usd to 36 pesos = 1 usd in something like one week.

You can actually see how the lira is losing against the usd since 2008.