If you use hotmail (hope not) or exchange email messages with hotmail users (who doesn't from time to time), for a number of weeks now messages sent via reply function in hotmail are often (not always) sent and received empty.

The problem is all msn hotmail.
To date, they are not sharing a solution.

The matter, including potential workarounds, is being discussed in various forums.
Here are links to just a couple of threads: