Linksys has frequent releases and I had the opportunity to stumble several times into firmware versions where some special applications (e.g. X-Window session over IPSec) wouldn't work. Turned out, they were playing with the MTU. Two releases further on, it would work, then again not etc.
I would rather try to solve the problem on the server side (make sure your server sends out unfragmented smaller packets).
/Martin
<Disclaimer>This is a private statement and does not necessarily reflect the opinion of my employer...</Disclaimer>