Has the validation on eMail field Changed ?

Has the validation on eMail field Changed ?

My users have been successfully using my applicaiton for over a year, but last week, an error message started to be displayed :
 
Enter a Valid Email address....
 
The address it doesn't like has an apostorphe in it (example john.o'reilly@domain.co.uk)
 
An apostorphe is a valid character (if it occurs in the name, prior to the '@' symbol)
 
Please advise if the checking routine has changed, as this worked and has worked for one year !
 
Thanks
 
Neil