runner beans

It may of been root disturbance from the origonal transplanting and therefore its set them back, or lasck of water form the beggining. It may be that its been so hot recently that they just haven't grown as much as normal as they have been affected by the heat.
Is the soil well dug or is there a hard layer underneath that the roots have hit and cant go down any more?

One of the reasons D & I don't start things in pots and then plant out is for this very reason... if you plant them out at the wrong time you will have a lot of problems. We just plant individual seeds directly into the garden once the soil is warm enough