I had the same problem, likewise only with a few of them. Fixed it by fitting a yoke made of thick plasticard strip over the push bar, held down by a pair of pins that were push fits into holes drilled in the baseboard. The strip is kept high enough gto stop the push bar rising up over the tiebar pin, but too low so as to prevent the tiebar moving freely. Crude but effective. Attached photo shows the arrangement, I hope.