Luckily, I don't appear to have had many of the problems that others on this board have experienced with 8.1 and overall I'm happy with the way it works. What I'm NOT happy with though isn't a bug but what seems to me the beginning of the gradual erosion of the Windows Phone 'identity'. With previous updates, all changes to the UI were consistent with their own design language and fitted with the OS well even if it meant that the features worked differently from the way they do on other platforms (that's what I liked about it, to be honest).
Now, I feel they've decided to trade the WP identity for a path where the OS is beginning to look and feel like an Android OS in an attempt to grab some of their market share. The Notification Centre, for example, although it works well enough, just doesn't look like it belongs in WP. The hubs too were an extremely important part of the WP 'identity' and the recent loss of most of those (with the 8.1 update), coupled with the increased reliance on (often inferior or poor quality) apps to fill the hole they left, all strip away what, for me, made it a true alternative to the 'big two'. Perhaps though, I'm wrong as uptake clearly hasn't been as great as expected thus far. I haven't even mentioned the rumoured adoption of Android apps running in WP which I believe would be the final nail in the WP coffin.
As a WP adopter from the beginning of the WP7 reboot - these things make me slightly sad (not too much - it's only a smartphone after all) and I'm wondering now, come my next upgrade, what my incentive would be to not just switch platforms and enjoy the extra features and apps that I'll be able to enjoy that are, in a lot of cases, not available to me now. I'm aware that the grass isn't always greener on the other side of the fence and that all the platforms have their foibles but even so...