# Mosaic augmentation appears to use images from validation/test splits

**URL:** <https://discuss.roboflow.com/t/mosaic-augmentation-appears-to-use-images-from-validation-test-splits/12299>\
**Category:** 🤝  Community Help\
**Created:** [June 13, 2026, 5:22pm UTC](https://discuss.roboflow.com/t/mosaic-augmentation-appears-to-use-images-from-validation-test-splits/12299 "2026-06-13T17:22:00Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![William\_Wan](https://yyz1.discourse-cdn.com/flex029/user_avatar/discuss.roboflow.com/william_wan/32/9621_2.png) [@William\_Wan](https://discuss.roboflow.com/u/William_Wan)\
**Post date:** [June 13, 2026, 5:22pm UTC](https://discuss.roboflow.com/t/mosaic-augmentation-appears-to-use-images-from-validation-test-splits/12299/1 "2026-06-13T17:22:00Z")

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```auto
Project ID: finalised-cymmt
Version: 2026-06-12 1:09pm
I generated a Roboflow dataset version after the images had already been split into train, validation, and test sets.

While inspecting the exported dataset, I found that a generated mosaic in the training split appears to contain images assigned to the test split.

This matters because training on mosaics containing validation/test images can inflate evaluation metrics.

```

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**Author:** ![system](https://canada1.discourse-cdn.com/flex029/uploads/roboflow1/original/1X/bb6edbfa56d0cf2ee603f061e9e09103502cc8cc.png) [@system](https://discuss.roboflow.com/u/system)\
**Post date:** [July 4, 2026, 5:22pm UTC](https://discuss.roboflow.com/t/mosaic-augmentation-appears-to-use-images-from-validation-test-splits/12299/2 "2026-07-04T17:22:18Z")

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