Warning message is not disappear after correcting mistake in subject when user composes PM

There are 2 issues related to warning message in field 'Subject':
1. Enter 1 character in field 'Subject', press button 'Preview'
Actual result:
Warning message is not appears
Expected result:
Warning message is appears 'Should be 2 - 120 characters'
2. Enter at least 2 characters in field 'Subject' and press button 'Preview'
Actual result:
Warning message 'Should be 2 - 120 characters' is appears
Expected result:
Warning message 'Should be 2 - 120 characters' is disappears
Situation is the same when field 'Subject' is empty