High Positive Pressure Observed when Opening Gas Cap?

Good Day,

I drive a 2008 Honda City 1.3L I-DSi. Recently I have observed when I open the gas cap, there is an excessive pressure present, and fumes of vapor is released out of the gas cap. I have read from forums that it's supposed to be a negative pressure sucking air in instead of a positive pressure.

Should I have my car seen by a mechanic or is it normal?

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