I've spoken with printers about this and you should have no problem printing on a 50/50 shirt.
I don't think it really matters when it comes to issues that may arise; both the 50/50 and 100% should be fine for plastisol.
I didn't base my decision on which shirts to use because of this but rather what shirts my customers would prefer and expect to see. The 100% cotton is a given and pretty much expected by people even when they may enjoy the feel of a 50/50 more. However, using a 50/50 may deter people and cost you some sales.
I use both, some customers like 50/50 for employee uniforms because they retain their color longer. Personally I like 100% cotton. If you cook 50/50 just a little to long transfers tend to take on the color of the shirt. They also have an unpleasant odor when heated.
I've had emails and phone calls asking if the shirts are 100% cotton (even though the site says that they are), but nobody's ever asked "do you carry 50/50 t-shirts". At least on the retail side of things.
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