Drum Roll notation question

I am trying to create a drum part that contains both a snare and a bass drum part, as would be common for marching and concert bands. I am having a bit of a problem with the notation results from MuseScore. Here is how I am doing it:

1. I created a line in the score for the drum part using the "5 line" option.

2. When adding parts, I start with the snare drum, and fill in the note values. I did this by highlighting the desired measure, go into Note Entry mode, and then select the acoustic snare option from the Drums pull down on the left side of the screen. I enter a whole note (in 4/4 time), tied to a quarter note in the next measure, followed by a half note and another quarter. All of these notations are on the third space from the bottom.

3. I then exit Note entry mode, go back to the 1st measure, highlight the measure, and enter Note Entry Mode again. I go to the drums pull down and select Bass Drum, and add a quarter note, quarter rest pattern - notes on beats one and three, rests on 2 and 4 for both measures. These are on the bottom space.

4. I leave Note entry mode. I want the whole note and half note to be rolls. I open the tremolo pull down, and select the 3 line icon without a stem. I drag it over to the whole note, it changes color to red, I release the mouse, and the tremolo marks disappear. Nothing on the page. So I go back to the tremolo pull down, select the three hash marks on the stem, and drag it over to the whole note, it turns red, and I release it. The marks appear on the score, but they are placed below the whole note, on top of the quarter note for the bass drum.

This is the problem - I cannot move the tremolo marks to the desired (correct?) position over the whole note. I click on the switch option from the menu bar (with the tremolo highlighted in blue) but nothing changes. I try to drag and drop them over the top of the note but that doesn't work either. If I try the same process on the half note, the tremolo marks appear as I would expect them to - on the stem of the half note which of course faces up.

Am I doing something wrong, or is this a bug in the software? I am running version 1.3; I initally saw the same behavior in 1.2, but nothing changed when I upgraded the software.

Thanks in advance for your help.