Since longer (several versions and now v4.7.0) I experience lag when editing files in kdevelop. For instance, if I move the cursor through a single line of text using the left- and right-keys of the keyboard, the cursor hangs occasional. This typically happens when it moves over a bracket, on which occasion the closing bracket gets highlighted. This suggests that the effect is related to the syntax highlighting or other parsing which takes place in the background. However opening the same file in kate directly, I do not see this behavior. I have seen this effect over a longer time on various occasions. Sometimes it seems to be there and sometimes not and I have not been able to pin-down its origin. It is very unpleasant and makes the use of kdevelop a pain, unfortunately. Of course I tried several changes like deactivating vim-input mode, syntax highlighting, various plugins, ...

Edit:
I wanted to add that the effect seems somehow related to the graphics system. By moving the cursor rapidly back and forth, I can easily get the CPU usage of Xorg above 20%, while it stays below 10% in kate.

Edit1:
Investigating further, I found that the problem depends strongly on the graphics driver used. When I use the recommended Nvidia driver (or older Nvidia binary drivers) for my NVIDIA Quadro NVS 4200M the lag is most pronounced. When I use instead xserver-xorg-video-nouveau the lag is visible but far shorter. Since my notebook has two graphics cards (Optimus) I have probably experienced the problem mostly with the Nvidia card. This is a pity because the general performance is much better with the Nvidia card and the recommended binary drivers.
I find it even stranger now that the issue appears with kdevelop but not with kate.