Updated the website link. Somehow overlooked that.
As for "opening in two applications simultanously", that's not a "software glitch", it's just common sense. Opening a file simultanously in two different applications in write mode will always lead to chaos, just don't do that or else you'll be responsible for everything bad that happens. For this purpose, most applications that open files for writing also automatically lock them (in fact, I think Windows does that automatically, which is probably why YY-CHR malfunctions, since it can only open the file in read mode after it has been opened in write mode by the hex editor).
There is a nasty software glitch where if you open graphics files with a hex editor (wxhexeditor), and open it using yychr (2 programs using the same file), yychr won't open it correctly. Also, why isn't this website query isn't link to this website: http://www.geocities.jp/yy_6502/ ?
Err. This is the .NET version of YY-CHR. It's different in some regards to the original, not .NET version we host here. It lacks the stamp tool for example, but it's an overall improvement of the original.