If you're paying in USD currency in eBay, thus your Paypal balance have to be in USD too. Suppose that you have top up wrongly in MYR currency, the system would not convert your MYR to USD currency and instead deduct it from your Mastercard.
If that is the case, withdraw out your MYR and top up again in USD. USD is being used internationally, even if you are paying in other currency such as AUS, EUR, Baht, MYR, etc.
But again be careful when using the top up function. You'll have 50% chance your top up will gone missing. There's no need to top up since you already link your card to Paypal which available for direct debit your savings account.
I wish not to topup my mastercard (it's a NEXG ambank card) because it takes time.
oh ok. i will try topup it back. cost me RM3 and another RM2..
EDIT: Thanks. it worked!