Problem description: The coercion of numbers to valid values in the JPEG export form is so quick that it interferes with entering the desired (valid) numbers.

Steps to reproduce:
1. export a drawing as JPEG
2. set the value in this field to 8.5 if it isn't already
3. put the insertion point to the left of the decimal
4. press backspace, then 4 

Current behavior:
the field passes through these states:
0.50
40.50

Expected behavior:
the field passed through these states:
.50
4.50
(note the factor of 9 difference)

Steps to reproduce another example:
5. Put 37 into the pixels/cm field if it isn't already
6. put the insertion point to the right of this number
7. Press backspace twice and then 50

Current behavior:
the field passes through these states:
3
3
35
350
   
Expected behavior:
the field passes through these states:
3

5
50           
(note the factor of 7 difference)