image thumbnail not be shown as expected

[Vincent]

There is an entity A1 with an image field, img. The preview size of the img field is small.
I uploaded the image file to that field of an record of A1 yesterday. There preview image was shown as expected. But When i browse that record today, the preview image is an broken image and i click that broken image, the full image of what i uploaded yesterday is shown.

How to fix this broken preview image? thanks.

Update:
Later, when i clicked the broken preview image, it shows a broken full image. Then I checked the data/upload folder, these is no file which name is equal to the image id.very strange behavior.

[yuri]

Never encountered. Could be problems on php side or elsewhere.

[Vincent]

Below is the full story
There is an entity A1 with an image field, img
There is another entity B1 with an image field, img

There is an one to many relationship between A1 and B1
when an A1 record, rec1, is associated to B1, the imgid of rec1 will be copied imgid of B1, as a result, an image preview can be shown in B1.

If I update B1 and make association to another record of A1, rec2, the imgid of rec2 will be copied imgid of B1, then image file of rec1 will be removed from data/upload, as a result, a broken image is show for rec1.

how can i prevent the image removal?

[Vincent]

Problem solved by replacing image field to Wysiwyg field in entity B1. The preview url of the image in A1 is set to the Wysiwyg field.