Prestashop Problems with Product’s Characteristic Length

I had to increase the size of the features on my Prestashop field. To do it I’ve changed column value on ps_feature_value_lang to varchar(1024) and after modify size in override/classes/FeatureValue.php to: ‘size’ => 1024

But I have this problem: every times I save the product, when I re-enter to modify it, the features lines are double than last time.

Each save pass for example from 2 features to 4, 8, 16, 32 ect.
It have custom value strings but doesn’t have selected function.

If I try to delete I have no result, on save featured double up anyway.

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