Hi!
I use 0.99.7739, but the described problem occurs for a long time.
Sometimes I open a document and then somewhere in the document a comma (decimal symbol) in an expression gets lost. This happens from time to time.
The marked number thirteen should be 1.3 (shown as 1,3).

Looking into the file, you can find "1,3". I think this number was not correctly saved as 1.3 (transformed to 1.3).
But I have a pdf of the sheet with correct results, so this must happen while saving.
<region left="315" top="801" width="200" height="66" color="#000000" fontSize="10">
<math optimize="2">
<input>
<e type="operand">Δσ.s.equ</e>
<e type="operand">Δσ</e>
<e type="operand">λ.s</e>
<e type="operand">1</e>
<e type="function" args="2">el</e>
<e type="operator" args="2">*</e>
<e type="operator" args="2">:</e>
<e type="operand">Δσ.s.equ</e>
<e type="operand">Δσ.s.equ</e>
<e type="operand">1,3</e>
<e type="operator" args="2">*</e>
<e type="operand">1.3</e>
<e type="operator" args="2">*</e>
<e type="operator" args="2">:</e>
<e type="operand">2</e>
<e type="operand">1</e>
<e type="function" args="4">line</e>
</input>
</math>
</region>
And furthermore a problem, which I think is related to the conversion . <-> , :
When I copy code an insert it somewhere else in the canvas or maybe in another line-block, the subscript "." is not rarely copied as ",". Even though the variable looks correctly with subscript.
So I get the message variable xy.sub is not existing. When I hover the mouse pointer over it I can see "xy,sub" with comma and of course that's something else than "xy.sub".
If you copy more lines than just a few, it can be really demanding to find the one wrong ",", because on screen everything looks fine.