I actually noticed a similar thing with my last cycle. I triggered, 34 hrs later did the IUI and the next day I got the eggwhite mucus. I don't think that they can test for ovulation once you've had Ovidrel but I'm not too sure I might be mistaken.
Well, I'm not the only one then!! I was doing IUI last year, and I ovulated before the trigger. The nurse told me this couldn't happen (it can), so I stupidly took the trigger and did the IUI. Of course it failed. The next IUI I did my IUI with three 20mm follicles. Went in for the IUI 36hrs after trigger, and I ovulated about 30 hours later. My RE now believes this did happen, and I'm now doing IVF, but I know the same thing could happen again. I think it means our follicles are not 'behaving' as they should be.