I have a form with a custom field, set to Single Line Text for the field type.
Maximum characters is set to 10.
When you cut and paste a value into the field on the form, it allows blanks to be entered, but they are not checked against the maximum character limit.
A value of 1234567890 is paste into the field, with a trailing space after the value - i.e. 1234567890<space>
The form allowed the space to be submitted, and should have counted it against the maximum count and saw that there was 11 characters and prevented the form from being submitted (and should have returned an error message).
Using GF Version 126.96.36.199.4