reply gives blank page

[michelnidaros]

I have a little issue.
otrs version 5.0.10
debian GNU/Linux 6.0

this is not always happening.
when i click reply on a ticket and choose reply(empty answer)
i write my freedback.
when i click on send mail

the next page is blank.
when i close this window and do a refresh.
i can see the freedback in the ticket.

but if i check my mail logs no mail is send,
in the admin panel from otrs logs nothing is seen.

when i do it again. everything is ok. no blank page and mail is send.

i have no clue where to search for this problem.