Highlighted area on track during trimming acting weird

Hi-

I'm working on a 35mm feature and lately when I select a cut to be trimmed, quite often I can click and the area is selected but the shadow on the track doesn't appear. Sometimes if I change the size of the timeline, the shadow appear, but not always. This is happening more and more lately. Is there some solution? Is it also related to the problem where I've done an asymetrical trim across 8 tracks and then when I'm done, the shadow remain, no matter what function I change to, until I resize the timeline. Is there a refresh problem with my cinema display or something?

Thanks.