LDAP Authentication fails if password has special (acceented) characters

The plugin for ldap authentication is enabled, one users has a password with accented characeters ("à"). Login fails (the error message is "wrong credentials").
Login works for other users.

In log file there is the following exception:

apr 14, 2015 4:41:46 PM org.camunda.bpm.engine.rest.exception.ProcessEngineExceptionHandler toResponse
AVVERTENZA: org.camunda.bpm.engine.impl.identity.IdentityProviderException: Could not connect to LDAP server
at org.camunda.bpm.identity.impl.ldap.LdapIdentityProviderSession.openContext(LdapIdentityProviderSession.java:117)
at org.camunda.bpm.identity.impl.ldap.LdapIdentityProviderSession.checkPassword(LdapIdentityProviderSession.java:284)
at org.camunda.bpm.engine.impl.cmd.CheckPassword.execute(CheckPassword.java:37)
at org.camunda.bpm.engine.impl.cmd.CheckPassword.execute(CheckPassword.java:24)
at org.camunda.bpm.engine.impl.interceptor.CommandExecutorImpl.execute(CommandExecutorImpl.java:24)
at org.camunda.bpm.engine.impl.interceptor.CommandContextInterceptor.execute(CommandContextInterceptor.java:97)
at org.camunda.bpm.engine.spring.SpringTransactionInterceptor$1.doInTransaction(SpringTransactionInterceptor.java:42)
at org.springframework.transaction.support.TransactionTemplate.execute(TransactionTemplate.java:130)
at org.camunda.bpm.engine.spring.SpringTransactionInterceptor.execute(SpringTransactionInterceptor.java:40)
at org.camunda.bpm.engine.impl.interceptor.LogInterceptor.execute(LogInterceptor.java:32)
at org.camunda.bpm.engine.impl.IdentityServiceImpl.checkPassword(IdentityServiceImpl.java:99)
at org.camunda.bpm.webapp.impl.security.auth.UserAuthenticationResource.doLogin(UserAuthenticationResource.java:93)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)