Mode_switch woes

Can someone help me here? I'm using XFree86 4.3 on a laptop. I am trying 
to use the us_intl keyboard (deadkeys). All of the special characters 
finally work, which i have never managed to see before! For example, if 
i do circumflex and c, i get a c with a circumflex on top. It hard to 
explain my problem, since i'm not sure about the terminology. Consider 
the following two lines from xmodmap output:

xmodmap -p
mod3	Mode_switch (0x71)

xmodmap -pke
keycode 48 = dead_acute dead_diaerisis apostrophe quotedbl

(Note that i had to modify Alt_R (0x71) to map it to mod3 Mode_switch.) 
When i type Alt_R apostrophe, an apostrophe should be typed, but in 
actuality nothing happens.

Why won't Mode_switch work? On my desktop, which runs XFree86 4.2, i 
have the opposite behavior. Only the most common non-ASCII characters 
will be inserted. (For example, e circumflex but not c circumflex.) 
However, with the exact same setting for Alt_R (mod3 Mode_switch (0x71)) 
when i type Alt_R and apostrophe, an apostrophe is typed.

Leston