I tried as you recommended... Removing the hyphens and placing the suffix before the image number, and beginning the numbering with the numeral 1. No change...

Just for kicks I also tried removing the numeral altogether:
images/lexingtonbedroom.jpg
images/lexingtonbedrooma.jpg
images/large/lexingtonbedroom.jpg
images/large/lexingtonbedrooma.jpg

Weird right? I know the system is working to some degree, because when you select "View Image" through your browser and check the path, it shows
images/medium/lexingtonbedroom_MED.jpg

Files are curently named:
lexingtonbedroom.jpg
large/lexingtonbedroom1_LRG.jpg