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(TMZ) - Nicki Minaj CLAIMS her dress was unzipped during her performance at the VMAs because she didn't have enough time to get ready ... but according to TMZ -- she pulled the same stunt during rehearsals.

[PHOTOS: Best And Worst Dressed on the 2014 VMA Red Carpet]

Eyewitnesses who watched Nicki's rehearsal Sunday morning tell TMZ ... she walked on stage wearing the same dress -- unzipped. One eyewitness says it caught her eye because she initially thought Nicki had come out in a robe.

[RELATED: VIDEO: Nicki Minaj's Wardrobe Malfunction At The VMAs]

TMZ says Nicki was wrapping her arms around the dress in a "weird" sort of way ... trying to manipulate it to see how much would be exposed.

And TMZ reports ... the VMAs created a make-shift dressing room right off stage -- draped with black sheets -- so she would have enough time to change.

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