Once in a while when I perform an action with an item, such as feeding it to a pet, the whole page goes blank. The page address is correct and the action seems to have performed, I just don't see the result directly. This has also happened when completing quests and when buying an item via the shop wizard (I don't remember whether it was user shops or NPC shops or both).

I have the same problem with Trades. Can't see anything! I'd like to cancel one of my offers and get my sP back! .___.

I have had that happen before as well at times when picking up pets from the training school or putting an item into your vault ^_^.
I was trying to purchase a slots trading card from a user shop and the entire page went blank and this error of text popped up on the screen where the shop search was supposed to be:

Application Error

An error occurred in the application and your page could not be served. Please try again in a few moments.

If you are the application owner, check your logs for details.

Is anyone still experiencing this?

I personally haven't had this problem recently. Not sure since when exactly.