This is a recent problem for me. When I open a model and start sketching or editing, I can double click on sketch dimensions to edit them as expected. However, I am finding that if I switch windows to a different model and then come back, I can no longer double click to edit dimensions. THe only way to edit them is to go to the dialoge box on the left, highlight the current value and then change it. This is also a problem for any new dimensions. Instead of allowing me to type the value after creating the dimension, I have to go back to the dialogue box on the left. The only solution I have found id to close the model and re-open it.
This is VERY frustrating. Anyone having the same problem or perhaps a solution?