Bug description

When overfitting on a single batch and defining dataloaders in class, the batch provided to the validation step is different from the batch on the training step. I was told in the slack community that this is NOT the intended behaviour.

How to reproduce the bug

import pytorch_lightning as pl
import torch_geometric
import torch

dataset = [torch_geometric.data.Data(x=torch.tensor([i])) for i in range(10)]
val_dataset = [torch_geometric.data.Data(x=torch.tensor([j])) for j in range(10,20)]
class LitModule(pl.LightningModule):
    def __init__(self):
        super().__init__()
        self.param = torch.nn.Parameter(torch.tensor([0.]))
    def train_dataloader(self):
        return torch_geometric.loader.DataLoader(dataset, batch_size=2)
    def val_dataloader(self):
        return torch_geometric.loader.DataLoader(val_dataset, batch_size=2)

    def training_step(self, batch, batch_idx):
        print('train', batch.x)
        return torch.nn.functional.mse_loss(self.param,torch.tensor([1.]).to(self.param))

    def validation_step(self, batch, batch_idx):
        print('val', batch.x)
        return torch.nn.functional.mse_loss(self.param,torch.tensor([1.]).to(self.param))

    def configure_optimizers(self):
        optimizer = torch.optim.Adam(self.parameters(),
                               lr=.0001)
        return optimizer

litmod = LitModule()
trainer = pl.Trainer(
    overfit_batches=1,
    accelerator='cuda',
    max_epochs=20,
    check_val_every_n_epoch=10,
)
trainer.fit(litmod)
print(litmod)

The val batch is the [10,11] tensor, the train batch is the [0,1] tensor

### Environment

• CUDA:
  • GPU:
    • NVIDIA GeForce RTX 3080 Laptop GPU
  • available: True
  • version: 11.6
• Lightning:
  • pytorch-lightning: 1.7.7
  • torch: 1.12.1+cu116
  • torch-cluster: 1.6.0
  • torch-geometric: 2.1.0.post1
  • torch-scatter: 2.0.9
  • torch-sparse: 0.6.15
  • torch-spline-conv: 1.2.1
  • torchaudio: 0.12.1+cu116
  • torchmetrics: 0.10.0
  • torchvision: 0.13.1+cu116
• Packages:
  • absl-py: 1.2.0
  • aiohttp: 3.8.3
  • aiosignal: 1.2.0
  • anndata: 0.8.0
  • astroid: 2.12.10
  • astunparse: 1.6.3
  • async-timeout: 4.0.2
  • attrs: 22.1.0
  • blinker: 1.4
  • brotlipy: 0.7.0
  • cachetools: 5.2.0
  • certifi: 2022.9.24
  • cffi: 1.15.1
  • charset-normalizer: 2.1.1
  • chex: 0.1.5
  • click: 8.0.4
  • colorama: 0.4.5
  • contourpy: 1.0.5
  • cryptography: 37.0.2
  • cycler: 0.11.0
  • dill: 0.3.5.1
  • distlib: 0.3.6
  • dm-clrs: 1.0.0
  • dm-haiku: 0.0.8
  • dm-tree: 0.1.7
  • etils: 0.8.0
  • filelock: 3.8.0
  • flatbuffers: 1.12
  • fonttools: 4.37.3
  • frozenlist: 1.3.1
  • fsspec: 2022.8.2
  • gast: 0.4.0
  • google-auth: 2.12.0
  • google-auth-oauthlib: 0.4.6
  • google-pasta: 0.2.0
  • googleapis-common-protos: 1.56.4
  • grpcio: 1.49.1
  • h5py: 3.7.0
  • idna: 3.4
  • importlib-metadata: 4.11.4
  • importlib-resources: 5.9.0
  • isort: 5.10.1
  • jax: 0.3.21
  • jaxlib: 0.3.20
  • jinja2: 3.1.2
  • jmp: 0.0.2
  • joblib: 1.2.0
  • jsonschema: 4.16.0
  • keras: 2.9.0
  • keras-preprocessing: 1.1.2
  • kiwisolver: 1.4.4
  • lazy-object-proxy: 1.7.1
  • libclang: 14.0.6
  • llvmlite: 0.39.1
  • markdown: 3.4.1
  • markupsafe: 2.1.1
  • matplotlib: 3.6.0
  • mccabe: 0.7.0
  • mkl-fft: 1.3.1
  • mkl-random: 1.2.2
  • mkl-service: 2.4.0
  • msgpack: 1.0.4
  • multidict: 6.0.2
  • natsort: 8.2.0
  • networkx: 2.8.6
  • numba: 0.56.2
  • numexpr: 2.8.3
  • numpy: 1.23.3
  • oauthlib: 3.2.1
  • opt-einsum: 3.3.0
  • optax: 0.1.3
  • packaging: 21.3
  • pandas: 1.5.0
  • patsy: 0.5.2
  • pillow: 9.2.0
  • pip: 22.1.2
  • platformdirs: 2.5.2
  • promise: 2.3
  • protobuf: 3.19.6
  • pyasn1: 0.4.8
  • pyasn1-modules: 0.2.8
  • pycparser: 2.21
  • pydeprecate: 0.3.2
  • pyjwt: 2.5.0
  • pylint: 2.15.3
  • pynndescent: 0.5.7
  • pyopenssl: 22.0.0
  • pyparsing: 3.0.9
  • pyrsistent: 0.18.1
  • pysocks: 1.7.1
  • python-dateutil: 2.8.2
  • pytorch-lightning: 1.7.7
  • pytz: 2022.2.1
  • pyu2f: 0.1.5
  • pyyaml: 6.0
  • ray: 2.0.0
  • requests: 2.28.1
  • requests-oauthlib: 1.3.1
  • rsa: 4.9
  • scanpy: 1.9.1
  • scikit-learn: 1.1.2
  • scikit-misc: 0.1.4
  • scipy: 1.9.1
  • seaborn: 0.12.0
  • session-info: 1.0.0
  • setuptools: 65.4.1
  • six: 1.16.0
  • statsmodels: 0.13.2
  • stdlib-list: 0.8.0
  • tables: 3.7.0
  • tabulate: 0.8.10
  • tensorboard: 2.9.1
  • tensorboard-data-server: 0.6.1
  • tensorboard-plugin-wit: 1.8.1
  • tensorboardx: 2.5.1
  • tensorflow: 2.9.1
  • tensorflow-estimator: 2.9.0
  • tensorflow-io-gcs-filesystem: 0.27.0
  • tensorflow-metadata: 1.10.0
  • termcolor: 2.0.1
  • tfds-nightly: 4.5.2.dev202204190046
  • threadpoolctl: 3.1.0
  • toml: 0.10.2
  • tomli: 2.0.1
  • tomlkit: 0.11.5
  • toolz: 0.12.0
  • torch: 1.12.1+cu116
  • torch-cluster: 1.6.0
  • torch-geometric: 2.1.0.post1
  • torch-scatter: 2.0.9
  • torch-sparse: 0.6.15
  • torch-spline-conv: 1.2.1
  • torchaudio: 0.12.1+cu116
  • torchmetrics: 0.10.0
  • torchvision: 0.13.1+cu116
  • tqdm: 4.64.1
  • typing-extensions: 4.3.0
  • umap-learn: 0.5.3
  • urllib3: 1.26.12
  • virtualenv: 20.16.5
  • werkzeug: 2.2.2
  • wheel: 0.37.1
  • wrapt: 1.14.1
  • yapf: 0.32.0
  • yarl: 1.8.1
  • zipp: 3.8.1
• System:
  • OS: Linux
  • architecture:
    • 64bit
    • ELF
  • processor: x86_64
  • python: 3.10.4
  • version: #202203181321-Ubuntu SMP PREEMPT Fri Mar 18 13:28:32 UTC 2022

### More info

_No response_

cc @justusschock @awaelchli