(false?) error registering payment

Hello,
inserting an invoice payment, with or without decimals, after click on PAY button, a line with error message can appear.
The error appears only when there are >1 invoices to pay, and it is displayed in n lines equal to the n invoices with payment field empty.
Example: if I have 5 invoices from a supplier and I fill the value to to pay only one, 4 error lines are displayed.
A single invoice to pay don’t generate any error.
The message is:
Warning: A non-numeric value encountered in /…/htdocs/fourn/facture/paiement.php on line 141

But everything goes well.

Thank you

to explain you better, see the image

Pièces jointes :