We are seeing problems with ignored priorities in the plugin, so I decided to make the simplest test I could think of:

Start a build on one machine with only one executor that runs for half a minute.
While it is building, start 2 builds of jobs with varying absolute priorities set, 1 and 2.
Watch in which order the other builds are run.

Everytime I do this test, the builds are executed in FIFO order, with no concern of priority.
If I repeat this test with the older priority mechanism of the plugin, it works like it should.