Continuity mistake: When Chris and Lydia discover that Mrs. Doubtfire is really their father, he explains Uncle Frank's and Aunt Jack's part in it. When it cuts back to Lydia, she has a long length of hair down the front of her right shoulder, but in the next shot, when she says, "It's really you in there," the hair is suddenly behind her shoulder.
Other mistake: At the start of the film we see Gloria Chaney, the Hillards' neighbour, drop a rabbit at her feet and then shout 'shoo' at it whilst pushing it with a brush. If she had it in her hands, why didn't she just drop it outside of her garden, instead of at her feet, making her have to push it to get it out of her garden?
Continuity mistake: When Mrs Doubtfire is pouring the cayenne pepper into Stu's dish of jambalaya, you can see that the container has nothing on the side, but when Mrs Doubtfire has finished, a label has suddenly appeared.
Continuity mistake: Mrs. Stelner visits Mrs. Doubtfire's apartment. She is in front of a mirror and there are three separate pictures of the three children in a triangular position with Lydia at top left, Natalie below her and Chris to their right. Later on in the scene after Mrs. Doubtfire watches her mask get flattened by a truck, Mrs. Steiner is still standing by the mirror. Natalie's pic has been repositioned on top of Lydia's pic, so they are now reversed. The framed picture is also moved.
Continuity mistake: When Daniel (dressed as Mrs Doubtfire) is at the pool bar drinking, the bartender is wearing a black suit jacket. In the next scene, he is wearing a white suit jacket.
Continuity mistake: When Mrs. Doubtfire is cooking for the first time, she drops the basil into the pot. The plastic piece that falls into the pan disappears.
Visible crew/equipment: When Daniel is having a spaghetti dinner with Chris, Lydia and Natalie in his flat, you can see the equipment crew reflected in the picture frame before we see the family eating.
Continuity mistake: When Daniel/Mrs Doubtfire goes to the bathroom after his false teeth fell out in his wine glass, you can see he is holding the teeth before entering, but when he is in the bathroom, the teeth have disappeared.
Continuity mistake: When he's in the empty studio playing with the dinosaurs there is a picture of a spider on the wall behind him that keeps moving.
Continuity mistake: In the restaurant scene, just after Miranda takes Natalie to the bathroom, Lydia picks up her menu and opens it just a crack. Then Mrs. Doubtfire starts talking and the camera cuts to a closer shot, and the menu is suddenly all the way open. (01:33:00)
Other mistake: In the Bridges restaurant scene when Mrs. Doubtfire enters the ladies room stall to change into Daniel, you hear a loud rip and Mrs. Doubtfire screams "damnit!" - however, when we see Daniel and Mrs. Doubtfire throughout the rest of the restaurant scene, neither of their clothes are ripped anywhere.
Factual error: The piano was invented by Bartolomeo Cristofori in the year 1720, in the 18th century. Miranda recommends a "17th-century grand piano" for Stuart's bed-and-breakfast inn.
Answer: Daniel was pretending to be different people that were just all very horrible, so he used different accents. This way, when the "British nanny" calls, he was hoping Miranda would instantly consider him. If he called pretending to be Ms. Doubtfire right away, she might not have basically given him the job right away. And if he used the charming British accent for all his characters, it would have lost its charm when he decided to be Ms. Doubtfire.
Bishop73
Basically this. He wanted Miranda to be frustrated by the other calls, so that Mrs. Doubtfire would seem like a refreshing change.
Azalea