I can navigate to the page even though there is a validation error(regular expressions)

On an interface, I am setting the following validation using regular expressions.

The format is [3-digit number] - [4-digit number].

Therefore, for example, if I enter a phone number like "080-0000-0000" here, a validation error will occur as shown below.
Naturally, when I press the button, it doesn't submit and it stays on that page.

However, a phenomenon occurred where nothing was submitted and the page changed.
Since it cannot be reproduced, it is difficult to determine the cause.
Do you know the cause?

(Sorry for the screenshots written in Japanese.)