When I enter 3xy the number 3 comes out in italics. Is this a bug?

When I enter 3xy the number 3 comes out in italics. Is this a bug?

Not really. What happens here is, that Math uses multi-letter variables, which are common in some disciplines, like economics. The rule is that a variable consists of a sequence of letters, numbers and dots (the first character can not be a dot).

So when you enter 3xy this is considered a variable - and variables are typeset in italics. The only odd thing here is, that a variable can start with a number.

The correct way to enter the expression if you mean 3 times x times y is 3 x y (with spaces between the characters).