I currently have a dual-head setup with the heads located above each other, instead of the more conventional left-right setup. When a break is imminent, prelude windows appear, each displayed at the center of the monitor (ok). 

After some time, they are supposed to jump to the top of the screen. At that point, they both jump to the top of the top screen, which shows two overlapping prelude windows. When you hover the mouse over them, they jump down to the bottom of the top monitor (though not at the exact same location, because my two monitors have different resolutions.

If you'd rather look at a picture than decipher the 1000 words above, please take a look at the attached screenshot.

Created attachment 187
picture to replace 1000 words

Fixed in: http://github.com/rcaelers/workrave/commit/06226efaeb746a05629563d19ed6f0df28ba4666

Sigh...
I apologize for being mistaken. There is one more case that isn't yet covered correctly.

I have two displays side-by side, with the right display a lower vertical resolution. Both screens are bottom-aligned (see picture 2). When a micropause is imminent, preludes appear. When it is time for the preludes to jump to the top of the screen, the prelude on the right monitor disappears. I suspect it jumps to the black area in picture 2. 

Strangely enough, if you use the mouse to "push" the right prelude window to the top of the screen, it is displayed correctly. So this happens only for the "timed" jump to the top, not for the "pushed" one.

Tested using the daily build of may 16th or thereabout.

Created attachment 188
Picture 2

Fixed in commit 1e55e392f8d13c60230c930843e9de9c7bdd589b