What does your OracleCommand.CommandText look like?
This is the CommandText property:
"-- First line comment\r\n-- Text with :unitName\r\nSELECT\r\n :unitName\r\nFROM\r\n DUAL\r\n"
I was able to reproduce this problem. I filed Bug 19433348 on your behalf.
The circumstances under which the bug occurs are fairly easy to work around.
1) Remove the colon in the second commented line.
2) Add a space between the the "\n" and "--".
If you do either of these things, you will not encounter the buggy behavior.