In addition to my address book, I have a LDAP server set up. The problem only occurs when the LDAP is reachable (i.e. if I am inside our company network). When writing a name in the To: field, KMail is able to autocomplete. Let's assume we have "Joe One <joe.one@company.invalid>" and "Joe Two <joe.two@company.invalid>" in the address book. After typing "Joe" KMail would now show the drop down menu with Joe One and Joe Two, and I can select them via arrow keys or with the mouse. Also, when typing "<space>T" or "<space>O" very fast, I am able to select any of them. However, when typing <space> only, then KMail will delete the space after maybe half a second. So if you are not fast enough, you will be looking for "JoeT" (who does not exist). This is especially annoying because sometimes you have to wait until the drop down address suggestion appears. KMail should not remove these spaces. When the LDAP is not available, I seem to only have completion of recently used addresses - and they just show the email address without the name. So in this case there are no spaces and thus the problem does not show up. Reproducible: Always
This bug has only been reported for versions before 4.14, which have been unsupported for at least two years now. Can anyone tell if this bug still present? If noone confirms this bug for a Framework-based version of kmail2 (version 5.0 or later, as part of KDE Applications 15.12 or later), it gets closed in about three months.
Just as announced in my last comment, I close this bug. If you encounter it again in a recent version (at least 5.0 aka 15.08), please open a new one unless it already exists. Thank you for all your input.