XMPlay seems to cut the note off due to Fxx command in another channel. FT2 doesn't do this, nor any other XM player I tried.
Attached a testcase. "with Fxx.xm" cuts the note off in XMPlay, while "No Fxx.xm" doesn't.
Here's the original XM I noticed this in:
http://modland.com/pub/modules/Fasttracker%202/Smirk/rose%20cube.xm (Position 2, Channel 4 & 6)
Edit: Sorry didn't realize there is a bug thread I could have posted to, feel free to delete this thread and I can repost there (I might have a second bug anyway).