anyone ever have an issue with not returning tourist cards?

There is no answer to your question. In the past you could just toss the FMT. There was no record keeping. But now the tourist permit is tied to your passport in the Migra computer. Last time I crossed going south I was told that soon there will be a booth on the northbound side to collect the permits. In the meantime they could be tracking expired permits. Or not!

Moisheh