Single, spaced bold text characters in staff text comments are joined after re-opening a doc

Here is the scenario in detail.
Suppose I have a basic score on a grand staff with a mixture of quarter, 8ths and 16th notes - a "typical" Bach/Handel 2-voice polyphonic texture for keyboard.
I'm doing intervalic analysis, that is I'm adding harmonic interval values between notes of the 2 voices. I'm entering these values as text in a group of 4. Of the 4 consecutive numbers in a group, for instance '6 3 4 3' some are marked in bold to show them as essential intervals.
When I finish entering the values I save the file. Everything looks fine before I close it. Once I re-open the file the bold characters that appear next to each other are joined together.
For instance, if in the previous text example '6 3 4 3' figures 6, 3 and 3 were in bold and 4 in regular font (not bold) on re-opening the file the text would look like '63 4 3'.
That means that if between two bold figures like 3 and 3 in my example there was placed a figure that is not bold, in this case 4, the spacing between all three figures would not be disturbed.

However, when I fix the spacing between bold characters on re-open and then close and re-open it againg everything stays as expected. The problem is only evident on the first 'save-close and re-open'.

I'm attaching 4 files:
- three jpegs showing the process of entering the figures
- a MuseScore file that is originally saved and re-opened with the bold figures' spacing disturbed