Created attachment 287053 [details]
sample file that show the issue

please take a look at this screencast:

http://195.250.34.59/temp/Screencast.webm

you can see gedit and geany using the same text file (605000 lines, attached):

- geany quickly load the file and show all its contents, you can navigate ecc.. with no issue
- gedit take a long time to load the file, the loading progress bar show that the file is loaded, but this is not true, scrolling to the end you can see the loading is still in progress, while loading gedit is not fully responsive (for example you cannot close it) and cpu usage is 100%
- please note how line numbers are show in geany and how in gedit (but this is probably another issue)

with files larger than the one attached cpu usage is 100% for long time (several minutes), the same file show in geany in less than 1 second