PlainCards vs. U-turn printer

I bought these to use with my Lexmark C510 color laser printer, with an add-on duplex thingy. I had mixed results. First time through, all the cards zipped through unscathed, no problems. But I did get some paper jams for the second side of printing, including ink smears, perhaps due to paper curling (none of the microperfs separated en route). I abandoned the duplexing and now flip over the stack and run it through a second time independently. I lose maybe 1 out of 10-12 sheets to jams. It's not a big deal to print out replacements, but it does add a little to the frustration/time/cost.