JSON_MIN export contains bounding boxes in transcriptions field

When exporting labels in the JSON_MIN format, sometimes bounding box information is added to the transcriptions instead of the transcriptions themselves.

To Reproduce
Steps to reproduce the behavior:
1. Go to LabelStudio
2. Label a bunch of documents
3. Go back to the project view
4. Click Export
5. Choose JSON_MIN
6. Exported json sometimes has bounding boxes instead of transcriptions in them like this:

```
{
"ocr": "\/data\/upload\/1\/filename.jpg",
"id": 22,
"bbox": [
{
"x": 12.924394307721723,
"y": 8.806096528365792,
"width": 17.47186637895714,
"height": 2.0321761219305667,
"rotation": 0,
"rectanglelabels": [
"Field 1"
],
"original_width": 2480,
"original_height": 3505
},
{
"x": 3.561753840591374,
"y": 64.35224386113462,
"width": 3.3507688945945233,
"height": 1.3547840812870442,
"rotation": 0,
"rectanglelabels": [
"Field 2"
],
"original_width": 2480,
"original_height": 3505
}
],
"transcription": [
"transcribed text 1\n\f", <------THIS IS CORRECTLY TRANSCRIBED TEXT!
{ <------THIS SHOULD BE ANOTHER TEXT, NOT A BBOX!
"x": 13.469188995051033,
"y": 54.451746318841145,
"width": 7.898240965829942,
"height": 1.5241320914479173,
"rotation": 0,
"text": [],
"original_width": 2480,
"original_height": 3505
}
],
"annotator": 4,
"annotation_id": 21,
"created_at": "2023-07-04T12:26:00.911143Z",
"updated_at": "2023-07-05T13:00:04.917034Z",
"lead_time": 1663.167
}
```

**Expected behavior**
I'd expect JSON_MIN to have the following format:
```
{
"ocr": "\/data\/upload\/1\/filename.jpg",
"id": 22,
"bbox": [
{
"x": 12.924394307721723,
"y": 8.806096528365792,
"width": 17.47186637895714,
"height": 2.0321761219305667,
"rotation": 0,
"rectanglelabels": [
"Field 1"
],
"original_width": 2480,
"original_height": 3505
},
{
"x": 3.561753840591374,
"y": 64.35224386113462,
"width": 3.3507688945945233,
"height": 1.3547840812870442,
"rotation": 0,
"rectanglelabels": [
"Field 2"
],
"original_width": 2480,
"original_height": 3505
}
],
"transcription": [
"transcribed text 1\n\f",
"transcribed text 2\n\f"
],
"annotator": 4,
"annotation_id": 21,
"created_at": "2023-07-04T12:26:00.911143Z",
"updated_at": "2023-07-05T13:00:04.917034Z",
"lead_time": 1663.167
}

```
**Environment (please complete the following information):**
- OS: Ubuntu 20.04
- Label Studio Version: 1.8.0

**Additional context**
I wonder if this is user error, or what may cause it, as it's impacting my data transformation scripts. I'm not expecting bbox information among my transcriptions. Also, it seems like the bboxes mostly happen when there's no actual transcription added, just empty text. But empty text is also important information in my use case.