Not so much a glitch as a "feature"...

The way it's always worked in the past (including for those of us who were premier on March 2 and Silver on March 3) is that you can always pick whatever seats you're entitled to whenever you access the seatmap, and they will stick unless something changes. So, if past performance is a predictor of future results,

1. you should be fine unless there's a schedule or aircraft change, at which point you would likely get booted back to E- (in fact, my wife has the E+ subscription now as well, and we have a reservation in December for which the equipment has change twice, and each time it's booted us back to E-, at which point I've had change our seats back to E+.)

2. If there is a schedule/equipment change and you lose E+, you can likely call and explain that you'd selected E+ seats when you were entitled to them, and they will likely return you back to E+... (had this happen a few times)

Dan