Something new appears to be going on with the credit and debit card companies. It is NOT transparent to the users.  I am having repeated troubles with Gift Visa debit cards that I use, and it is for different reasons every time, ususally involving temporary overcharges that reverse. 

What they are doing to Debit cards they are also doing to credit cards, it's just that most users don't see them like you do because the the games they appear to be playing are around charges that reverse. 

Most credit card users never check their statements regularly.

I NEVER heard of or encountered a tolerance amount until a couple of weeks ago.

I use the gift cards for safety - both for me and for the vendor. There is a fixed amount on the card which I know is there and if the card number gets leaked or out elswhere there is a limited finite amout that fraudsters can access.