vboxsf weird issue: a file can't be synced...
 

hi,
i have virtualbox running on ubuntu (both host and guest).
the guest runs ubuntu 10.10 and a shared folder is mounted at boot with:
mostro-Business /home/teo/Business vboxsf rw,uid=1000,gid=1000 0 0

no problems at all...

since 10.10 is a BIT outdated, i upgraded the guest to 12.04. everything works fine, except for a weird issue: sometimes, when a file is created on host shared folder, it does not appear on guest.

dropbox (running on host) creates and deletes an empty file in the shared folder.
it correctly appears and disappears for some hours (or days), then it's not synced anymore. no matter if i manually create it on host: it won't appear on guest...

i tried and change the filename: it ran fine for a couple of days and now it does not appear anymore...

any hint on how can i debug this?