above each button that enables the trigger there is a knob that you can dial, this one is for the note you want on that trigger. By default they should be set at c3.
However, if you have a patch downloaded or what not, chances are the designer might have set them different for a nice melody.
So check that first.
If that is note the case, and all notes are set how you want, then the problem probably lies with the envelope settings controlling a filter.
It may be so that the mod enevelope triggers a low pass filter (one of the 3 available) and stills decays after the second note.
I that case, you could shorten it.
In any way, just play around with it till it sounds good, and or do some researsch in envelopes and filters. Nifty stuff (if you dont have that knowledge already offcourse.)