pppoe secret problem

i have mikrotik 4.17 os on dell p4 2.8GH 512 Mb ram, 40 active users, the username and passwords i used are like
saf49945
a@$34th67*__f4 ( 14 character )
the problem i have that i added new users (30 others) like
ram6001
p@4+stvvcvf= ( 12 character )

when i try to connect using any one of them i get the error 691
(the remote connection was denied because the user name and password combination you provided is not recognized or the the selected authentication protocol is not permitted on the remote server)
i double check the username and password and the protocol and every think is ok.

i try to delete the last character in the password ( it is = here ) then it is work !!!
then i try to return the (=) and it is work too!!!
this happened with others new combination of secret i have ( delete the last one or two characters it is work then return them it is work but before deleting it dose not work )
do you think it is a bug in this version on mikrotik.

the 40 users i have are work directly without any think i do , i just copy them from my old 4.11 system on IBM 1.7 GH..

any idea please where is the problem???

thanks