Ms Yingluck arrived at polling unit No 32 at Khlong Lamchiak School in Bung Kum district at 8.10am amid an army of journalists from local and foreign news agencies and security officers.
The ballot papers for party-list votes are orange, while the ones for constituency voting are purple.
However, the caretaker leader placed the orange party-list ballot in a box with a clear sign in Thai which translates in English as “constituency system”.
She did the same with the purple constituency voting paper, putting it in another box that says “party-list system”.
It was reported that journalists were busy trying to get a good picture of Ms Yingluck casting her vote, while election officials were probably distracted by her appearance and failed to notice the slip.
It was only after Ms Yingluck had left the polling place that the press began to notice the irregularities in the photos they had taken.
The pictures of Ms Yingluck’s misplacing her ballot paper have gone viral in the social media and mostly drawn negative criticism against her.
Many internet users assumed that Ms Yingluck was probably too busy with posing and smiling for the cameras before placing her ballots and did not notice that she was putting them in the wrong boxes. Others thought the incident was an embarassing mistake that should not have been made by a politician with a position as high as prime minister.
Anti-government protest leader Suthep Thaugsuban was quickly to take a swipe at Ms Yingluck.
Election Commission officials said Ms Yingluck’s ballots remain valid despite the mistake.
A video clip, uploaded to YouTube by NaewnaOnline, shows the caretaker premier misplacing her ballot papers in the Sunday, Feb 2 election.