Such an issue was already reported by another users or ours, however, our department invested quite a while in investigating the possible reasons that might cause such an issue, with no avail. The provided information in this thread is also not enough for to trace this issue down. If you manage to get a scenario which will always replicate the undesired behavior, feel free to get back to us with it, so we can investigate it and address any possible issues. Until then I am afraid that there is nothing I can do about this.
Thank you for your time and efforts.
the Telerik team