After installing the latest release I also noticed that I was still seeing calendars being displayed underneath select boxes. After looking into this issue I noticed that the iframe wasn't being positioned correctly when the calendar was inside a container that had been positioned relative or absolute.

I added the following to my main stylesheet to position the iframe correctly for the above situation.

.ajax__calendar {
    position: relative;
}
.ajax__calendar iframe {
    left: 0px !important;
    top: 0px !important;
}

Note: I have not tested this under any other conditions.

Hopefully this helps.