Hello, I too use a FR305 and use the courses and waypoints plug-in. I love the plug-in and use it quite a lot however I find that for my device the plug-in does not reliably export the courses to the 305 so I have started created the courses using the plug-in, then exporting to file. I then import it to Garmin TC and then us this to upload to the FR305. I was surprised when doing this how few courses I can hold at once. The TC export tells me if I'm over etc so I would try seeing if you can do it correctly on TC and then if so then try it with the plug-in.
For predictability I do as I mention, create the course with the plug in and then export to file.
If I find out more I'll post it up
interested to hear from other FR305 users of courses.