Wow, that is indeed very annoying! I have looked into it and found a fix. The fix is quite funny: the property in .NET is called 'AutoWordSelection' and is already set to false for our text editors. However, setting it to 'false' again, fixes this issue... It will be part of the next Mendix 6 and 7 releases.
Update: Mendix 6.10.5 which contains the fix has been released. The next Mendix 7 version that we are working on right now will also contain the fix.
Where exactly do you have this issue because I can't seem to reproduce this behaviour. I can select single words / characters fine from labels, attribute names etc.
I share your frustration Martijn. Not only in Mendix but in every Windows application. Would indeed be great if Mendix would turn this nonsense off.
Ah, I get it now. That is really annoying indeed. As far as me or my colleagues can tell there is no way to change this behaviour. My advice would be to suggest this as an idea on the mendix idea forum (and hope they will pick it up).