Unison of different values. My problem or bug?

Hi all,
I'm trying to write a music sheet for a Giuliani's studio for guitar. It's written in two voices.
Forgive my english, i don't really know english words for music :)
My problem is that when I have an unison of different values, musescore plays only the shorter one, and not the longer one as i was expecting. I don't know if it is a bug of musescore or a misconfiguration of something or what.

Here goes the links to the sheet i was trying to write:
http://musescore.com/user/65404/scores/84242

In the second measure is written as it should be (I've confirmed it with my music teacher). The first "A" for example is an unison of 1/16 A and 1/2 A, i should hear the 1/2 A but i hear only the 1/16.
First measure sound has it should but is not the right way to write it.

Thanks in advance.
testo