Articulations in imported XML files not always honored

I've imported an XML file (original source: Sibelius) containing a flute part. It includes some staccatos, but they don't actually play. I've copied some sample to a new score. When played, it sounded as a piano instead of flute, so I had to change instrument. Surprisingly, then the staccatos played correctly.
In order to find out why, I saved both scores as MSCX and examined them with a text viewer. I've found that the original one lacked some basic information. All that was there is


<Instrument>
<longName>Flauta</longName>
<trackName>Flute (2)</trackName>
<Channel>
<program value="73"/>
<controller ctrl="10" value="63"/>
<synti>Fluid</synti>
</Channe>
</Instrument>


Basically, the MIDI ID of the Instrument and little more.

On the contrary, the other file, for which I had manually chosen the instrument, contained much more information, such as instrument range and, most importantly,


<Articulation name="staccato">
<velocity>100</velocity>
<gateTime>50</gateTime>
</Articulation>


This gave me the clue for the solution: To select manually the instrument.

However, I wonder why, in the absence of instrument information within the score file, it is not taken from the Instruments.xml file included with Musescore.