Problem with building

I keep having this problem in the pass few days. Whenever I stretch a prim, it returns to its original size or somwhere in between. Occaionally it will jump back to the stretched size.

Same with moving a prim. It just keep going back to its previous position. And when I change the prim texture or color, it will only change a few faces but not all.

Is it something wrong with SL? Or its only me? What could cause this?

It's probably lag, and it's either SL going borky (now there's a surprise) or a slow down at your "end", as it were (possibly to do with your connection to the net.)

Or perhaps a bit of both

I get it from time to time. Just one more annoying little SL niggle to deal with now and then.

Very possibly your network connection.
Do a bandwidth speed test at three of many easily found sites, is probably the quickest test.
Check for programs "connecting" behind your back.

Will try that. But I still don't understand, I don't feel any lag and has nearly 0% packet loss.