[TxMt] Bug in Filter Through Command?

I'm trying to use Filter Through Command, but it doesn't seem to be working right. For example:

1. Create a new document and add the characters "ABCXYZ" 2. Select all text 3. Go to the Text > Filter Through Command dialog 4. For the command, enter "tr -d X" 5. For the input, choose Selection 6. For the output, choose Replace Selection 7. Click Execute

Expected result: The selection changes to "ABCYZ" Observed result: Nothing changes

Is this a bug, or am I doing something wrong?

Note that the command appears to work for other output choices (e.g., Show as Tool Tip). It's only the Replace Selection option that's giving me trouble.

Trevor