I had a student inserting an image (that resided on the web) with an address that ended
Laughing_buddha_statue_Buddha_gift_m.jpg
The image showed up correctly in the editor but only the alternate text showed up in the preview. I tried shortening the name and then it showed up correctly. However, when I experimented to find out the length at which it failed I found I could add letters and numbers until it was way past its original length.
Further experimenting suggested length was not the issue but it was to do with the use of upper-case. In particular, if the name began with an upper-case letter it could not move away from upper-case and then back again; if the letter began with lower-case there was no such restriction. So, these are OK...
ABcde.jpg
ABCDE.jpg
abcde.jpg
aBCDe.jpg
aBcDe.jpg
But these are not...
ABcDE.jpg
AB_CDE.jpg
Ironically, the work-around for my student was to download the image, change its name and then upload the image...which meant running into the other set of problems.
However, I have since discovered the problem also disappears when CamelCase linking is disabled.
I am using 1.8.2