HP49-50G BOLD characters while writing prog with EMU48

[Gil]

Sometimes, when writing or editing a program with EMU48 (HP50G), I suppose that I touch a wrong key or sequence of keys.

Then the following text inside the program appears to be written in bold.

Precision:
The added / inserted text is put in a place where, previously, no bound characters was present.

It seems that, involuntary I use a shortcut to get the following characters to be written in bold.

Does somebody have an idea about that possible shortcut?
Or what my be happening?

Regards,
Gil