Please describe the problem:
When doing a 'save as' operation on a file in a directory containing several hundred to 2000 images, the amount of time for the dialog to display filenames and allow editing of the current filename can take up to about 30 seconds. 

Interestingly, it's not all the time as sometimes the display is nigh immediate as expected. 

Steps to reproduce:
Open an image from a directory that contains say 2000 images (each a JPG format, sized 4000x3000 pixels or thereabouts). 'Save as' an xcf file (the first save as seems to be fine). Do some editing, do another 'save as' operation to rename, this and all subsequent 'save as' seem to take a substantial amount of time. 

Actual results:


Expected results:


Does this happen every time?
It's pretty reproducible, but not quite 100% in any given operation. It 'feels' like the first save as after opening an image (I often control-1 to open the last variant saved so that I can flatten it and sharpen that version) seems to generate the file list at a normal speed, but that subsequent save as operations are slower. 

Other information:
My overall workflow is to generate several different image variants as I edit, saving as different xcf filenames, flattening each back to a single layer, before sharpening each variant and saving as a jpg. There might be a component to this performance issue which relies upon having several multi-layered xcf.bz2 files in the directory as well, but it seems to reproduce with only the jpgs as well. 

I've tried to change the dialog preference from displaying images to displaying files, but that doesn't persist at all.