(Cover) - EN Showbiz - Britney Spears doesn't appear very comfortable on the US X Factor judging panel.

The pop superstar co-judges on the hit TV talent show with Simon Cowell, Demi Lovato and L.A. Reid.

To onlookers' surprise, Britney seemed unusually restrained in her seat Friday.

"[Britney was] uptight," an eyewitness told Us Weekly magazine. "Her body language was reserved. Demi, Simon and L.A. seemed very relaxed and engaged with contestants and the audience."

It is rumoured that Britney was afforded unusual allowances, such as taking breaks whenever she wants, in the multimillion-dollar contract that she signed with Simon.

The songstress walked off set on her first day leaving an empty judging seat for over four contestant performances.

Britney is said to have taken another bizarre recess on day two.

"After a very popular contestant finished, Brit stood up and immediately walked towards the tunnel where judges enter," a source revealed to the publication. "Her bodyguards [and entourage] jumped up and ran after her. She was moving fast It was odd."

Britney contends that she's enjoying herself on the show.

"Britney walks off??? LOL was just taking a little break people. I am having the BEST time!!!" she posted on Twitter. (C) Cover Media