After Spencer loosens his tie and starts to take it off, the tie disappears. Taking into consideration Spencer does magic tricks, that's a pretty good one.
In several episodes, throughout the series, Spencer's apartment was shown to be in front of a staircase, leading down to the first floor. In this episode, there is an apartment door across from his apartment. He didn't move and still in the same apartment (everything inside is still the same). Didn't anyone on the writing staff know this??