"Pricing Field" of type "Product" doesn't validate

I have a "Pricing Field" of type "Product" which used to work. After I updated to GF v1.5.2.8 the form won't validate and gives this field the following error message: "Please enter a valid value".

The site's locale is Norwegian Bokmål (nb_NO)

I have the following settings:

• Field Type: Single Product
• Price: Kr 0,00 (gets filled in dynamically)
• Disable quantity field: unchecked
• Required: checked (tried to uncheck, but still doesn't validate)
• No Duplicates: unchecked

Advanced tab:

• Allow field to be populated dynamically: checked
• Name: productName
• Price: productPrice
• Quantity: productQty

Enable conditional logic: unchecked

These are my filters to populate the fields:

add_filter("gform_field_value_productName", "gnd_gf_populate_postTitle");
function gnd_gf_populate_postTitle($value){
	global $post;
	return get_the_title();
}

add_filter("gform_field_value_productPrice", "gnd_gf_populate_productPrice");
function gnd_gf_populate_productPrice($value){
	global $post;
	return intval(get_post_meta(get_the_ID(), '_gnd_publication_price', true));
}

add_filter("gform_field_value_productQty", "gnd_gf_populate_productQty");
function gnd_gf_populate_productQty($value){
	return 1;
}