There is a usability issue when replacing text between two styles. Replacing or
pasting text of one format (or without formatting) to a spot where it is
immediately preceded by text of another format is awkward at best (Demo I), or
impossible at worst (Demo II).

Please try the interactive demo (attachment), so you can see this usability
issue first hand.

This is a usability issue, not a crash report. That is, it is an issue with how
the user interface works, which makes it difficult for people using the
software, especially new users and people who simply expect their software to
work. The demos may be specific but they highlight general issues.

This usability bug hinders adoption of the software, and frustrates more
experienced users. Apart from hindering learnability, efficiency of use,
memorability, and subjective satisfaction, it also leads to more user errors.

Intuitive user interfaces do the “least surprising†behaviour. From a user's
point of view, the least surprising behaviour is the “correct†behaviour,
regardless of software's internal set of abstractions.